Oceana has relatively little variety of tech levels, at least among the settled humans and demi-humans. Ideas spread fast via ship, so that generally within a generation any idea has spread across the known world. The individual city-states and races will have different production capabilities, but that is generally due to local resources and temperment. The overall tech level of advanced city-states or races is at around the late Middle Ages compared to Earth's European continent. There are some strange tech anomolies on Oceana though. There are a number of advanced pieces of technology that were discovered much later in Earth history, but are actually simple to build or maintain.
Technological devices also move very quickly from the settled islands to the newly settled areas. This is similar to the United States west during the late part of the 1800s. People in the frontier areas tend to heavily tax adventuers, knowing that adventuers don't want to travel for weeks back to the older lands for simple supplies. This largess is then used to buy manufactured stuff from the older, settled lands.
The Greeks are known for both magical and mundane theory.
As with any fantasy world, there is the problem of keeping technology at a midieval level despite having continous civilizations that are as older than any single civlization on Earth. A number of factors determine overall tech levels for Oceana.
The first is neccesity. There will generally not a be any advances in technology unless there is a need for it. Note, that there is almost always a need for high productivity or less man power being used to do an existing job. Hence, effort will be put into improving existing items to make them more efficient. An example of this would be the transistion from matchlock guns to flintlocks. Along with neccesity there has to be the idea that change and improvement is possible. This is illustrated in David Drake's books "The Reformer" and "The Tyrant". On Oceana the imputus for change is that magic spells can be discovered.
Second is having a sufficient surplus of goods and educated people to actually try new things. This includes sufficient food or raw materials to use with the chance of having no return. Hence, subsistance agriculture will not generally try anything new and experimental with regards to farming since a failure would mean starvation.Along with trying new ideas, there is the need for basic research as Galileo or Newton did. Related to having a surplus of people is also haveing a lot of luck. It can take a lot of insight and genius to make leaps in technology. A large population doesn't mean lots of inventors, only the possibity of geniuses. The flip side to this though is that in a society like ancient Rome, the presence of cheap slaves and lack of an inheiritance framework held back the desire to create improvements. The Romans wouldn't generally try and invent a newer or bigger system, they would build a lot more of the same small ones. For example, instead of trying to build larger iron furnaces which would require research, they would just build more of the same small ones they had been using for generations.
Third is the presence of magic. Magic is in many ways another technology. In a magical world, people are as apt to look for a magical solution first as opposed to a mechical or chemical technology. Magic is more likely to shut off exploration into specific areas than to total eliminate innovation. Once a magic spell has been developed to solve a problem, there has to be a real incentive or demonstration of a superior non-magic technology to propel further research. This is especially true of basic research. Magical research can more easily lead to the creation of spell to solve a specific problem, but will not generate the basic scientific data to enable a technological advance.
Fourth, and unique to Oceana, is bleed over from Earth. Individuals and small groups from Earth are transfered to Oceana seemingly at random. There are a number of limitations on this. Most of the people are not engineers or even craftsmen. They do not know how a piece of their technology is made. They also don't usually know the local languages, wether Latin, Hebrew, Greek, Egyptian, Dwarven, etc.
Fifth, is being able to keep and diseminate discoveries. Improvements to an existing item are fairly easy to spread far and wide, such as the horse harness or stirrup. This happens in Oceana fairly fast with it's far flung maritime trade networks. The much tougher part is to share more abstract knowledge, and to keep such discoveries well known. It is the ability to eventually make connections that can lead to a lot of the modern inventions. Oceana has suffered in regards to keeping non-magical abstract knowledge. While paper has been discovered in the more civilized lands, there has been no printing technology until recently.
Oceana is primarily an ocean world. As such some maritime tech is fairly advanced beyond the normal mideval tech period.
Most societies use the marconi sail rig, catboat rig, or lanteen rig for small craft, usually under 20 meters in length. This permits small craft to sail to windward fairly easily and manuever quickly. All three sail rigging technologies are easy to replicate after being seen on visiting vessels. As such, any society that can make small vessels can use any one the three forms of sail rigs.
Larger oared vessels are fairly common all over the planet, and are useful for areas where the wind is often unpredicatable or weak. Such vessels are often used as couriers since combining a sail results in a vessel that is always able to move.
The larger city-states are able to make square rigged ships and schooners. Both types of sail rigs are fairly complex, as are the hulls. As such, only the larger and more capitilized societies are able make ships with such rigging and hull designs. In addition to having significant skilled workmen to build the ships, it takes skilled sailors to run the ships. Smaller city-states will build smaller vessels or buy the more advanced larger vessels from a larger island. The limitation is not so much the technology of making the vessel, but having the need and sufficient capital to make larger ships.
There are no steel hulled vessels, although some merchant ship's are covered with copper or lead to reduce fouling. There are no known steam driven vessels, nor is the technology known to have been implemented. Steam propulsion does exist as a theory. There are rumors that Dwarves have built steam powered ships, but no confirmation has been found.
Navigation is still fairly primitive. The geography of the world, with it's abundance of close together island means that celestial navigation is not required. Ship's can sail the length and breadth of the known world and never be more than a days sail out of sight of land. As such, dead reckoning and pilotage are the rule. The compass is in common use for civilized ships and is being sold readily to less advanced societies. The more civilized parts of the world, and the areas that civilized traders travel to frequently, are fairly well charted. Charts are expensive though. Light houses and wooden bouys are used in the more civilized and traveled parts of the world.
Canals are covered under ground transporation.
Ground transportation technology is fairly evenly spread out. Almost every society has full knowledge and access to the various technologies. Ground transportation consists mostly of foot, horse, rickshaw, chariot or horse drawn carriage or oxen pulled wagon. Horses are expensive due to the amount of land needed to keep them and generally are only seen on the large islands, in particular Egypt. Oxen are commonly used for plowing and similar traction tasks. Oxen provide both traction and milk from the cows and require relatively less feed.
The Roman style road is known by most settled human and dwarf societies, but only used outside the cities in the richest ones. The limitation on high quality Roman style roads is the man power, and thus expense, needed to build and maintain them. Except for the dwarves and some humans, most societies do not have sufficient trade, money and people to need decent roads.
The concept of the railroad is known but is not implemented except in few exceptional places. The limitation is again the lack of metals for the rails. There are no known plans for locomotives either. Rails made of wood or stone are common but awkward and rough on the wheels. As such they are rarely used. Most people that encounter such stone or wood rails will not automatically know what they are for.
Air transport is mostly magical based. There are kites and hot air ballons which are of course non-magical, but they are of limited use for travel or even observation. Flying carpets and brooms are relatively rare, but do exist. Flying adds an entire new dimension to warfare in Oceana. See the page on Ocean warfare for more details. Magical flight pre-dates the use of gunpowder.
The canal is known, although it is a spin off of Roman aquaducts and general irrigation technology instead of a much later seperate development. Canals are common on the larger islands, and to point of being ubiquitous on Egypt. Smaller islands usually don't have enough trade to warrent the investment. Roads are cheaper in the short run.
Long distance travel can also be accomplished by magical teleporation. This has only occured in the past 30 years.
Communications is fairly Colonial era with regards to non-magical communications.
Oceana has invented the printing press within the past 100 years. Paper has been around for over 1500 years, but is still very expensive and is partially cloth based. Wood is to valuable to use for just printing. Expensive books and such are printed on lamb skin vellum or parchment. Most areas of Oceana are illiterate. Freedom of the press exists in some areas, and is a concept known in most human and human friendly lands. Not all city-states permit a free press, but the concept is known.
Mass communications is limited to the printed word and live performances. Radio and television are known of as a concept to a limited number of people, but has never been tried. The concept has come from dimensional travellers rather than local research. As such the concept is not secret, but is not common knowledge. The percived cost of building the infrastructure has prevented anybody from trying to develop the theory.
Long distance communications is much tougher on Oceana. The semaphore tower (clacks) is well known and available on many of the larger islands. Intra-island communications is thus fairly fast. The clacks is both a day and night device. During the day the towers use flag arms. At night, they shift to lights using carbide to generate acetylene gas as the light source. Note that acetylene gas is very explosive, and occasionally a clacks tower will blow up. Also, the use of carbide lamps underground is subject to explosions if the party encounters mine gas (methane). The concept of the telegraph and telephone exist, but the expense of the copper keeps it a laboratory experiment instead of a viable technology. The lab sets are powered by chemical batteries since there are no generators availiable. The concept is known, but nobody has a working version; nor is anybody likely to bother.
Magic does play a role.
Oceana is relatively low tech when it comes to energy sources. Oceana has very little availiable coal and essentially no availiable oil. The primary energy sources are animal dung, wood, and charcoal as far as heating goes. There is extensive use of wind power via windmills, or falling water via water wheels. Coal is expensive and only used for metal working in the form of coke by the dwarves. The making of coke is a Dwarven secret, and will not be known by Dwarven adventuers. Peat is also expensive and generally not used. Peat is in limited supply and does not provide enough energy to be considered really worthwhile. Peat is used only in areas where it is found, but is often used extensively there.
Vegatable and animal oils are used for non-magic lighting. Beeswax, tallow and whale oil are commonly in use, albeit all but tallow are expensive. Rome and Greece tend to use olive oil or peanut oil.
The d20 / D&D continual flame spell exists. The implications of a permanent form of light have a great impact upon society.
Farming technology is fairly late 18th century tech level on the majority of islands. The northern European bread board or mold board plow is in use in most societies. Oxen are used for traction animals instead of horses. There is crop rotation and use of manure and fish waste (near the coast) for fertilizer. Plant and animal breeding is fairly common and at the level of early 20th century US or Europe. There are a variety of domestic animals including cows, sheep, goats, pigs, and various types of fowl such as turkeys, chickens and pidgeons. There are generally multiple breeds of each species instead of the small number of breeds seen in late 20th century Earth.
The richer and more advanced islands have horse or oxen drawn farm machinary similar to what was seen on US and European farms around the early part of the 20th century. This provides a significant boost in food production. Farm machinary is an export item, with islands that are big enough to use the equipment wanting to use it. The poorer islands do not have the capital or labor to actually make the equipment, but can use it and have the basic knowledge of making it. Note that there was a form of mechanized horse drawn machines in use in early AD according to Pliny. That came from Gaul, was invented in Oceana without Earth tech.
Irrigation is in common use, but is limited by geology. Windmills exist and are used along with reservoirs and aquaducts. The water meadow, invented in England in the mid 1600s is in use in many parts of Oceana. The water meadow yields more hay and similar grass type feed crops for animals. Water powered grist mills are normal. The multi-field system of clover, turnip, fallow, etc is normal. This is circa 1720 England.
In Rome and Greece yeoman farmers, ala early Rome and Greece, own the land. This is different than say England circa 1720.
Fishing is a major source of food most islands. Hand hauled nets and long lines are the common way to catch fish. Lobster and crab pots are common along coastal areas and inside harbors. Whaling and sealing are common for the advanced societies, with most whaling being done in the open oceans to the east of the islands. Only the relatively advanced societies can do whaling voyages, with the less advanced islands doing only coastal whaling. Whale oil is mostly used as a lubricant or for lighting.
Food stuffs are fairly well traded although out of season and out of climate foods are expensive. Salt is cheap, and made using evaporative vats similar to American colonial practice. Spices and pepper are readily availiable albeit pricy. Food is stored by salting, pickling and smoking mostly. There is limited refrigeration. Ice houses are common in more northern lands and some ice is shipped south for the nobility. The wooden barrel is in use, along with the clay amphora.
Primogeniture is the norm. Only the eldest son will inheirit property. Although this is tempered by not allowing farms to be be joined into single bigger farms. If the father had gotten two farms, then the oldest two sons would each get a farm. This prevents farms from being divided into marginial operations. And to prevent concentration of land into just a few people.
Metal working is fairly advanced, roughly fifth decade of the 1900's on Earth's time line in terms of quality and types of metals except for the lack of aluminium. The best metal working, especially steel and iron, is done by the dwarves. The lathe, drill press, milling machine, shaper and other early 20th century machine shop equipment exist and are used, although mostly by the dwarves. All such equipment is hand operated, or at best jig operated. It is also water powered or hand powered, not electrically powered.
While the metalurgy is advanced, the amount of metals produced is not. Overall metal production is that of the 1300's Europe. The major limitation is lack of access to sufficient heating materials and lack of access to sufficient amounts of various ores. Coal is only found in small deposits. Most ores are also only found in small deposits. Charcoal is made from trees which are needed for many other uses such as home cooking, ship constuction & repair, glass making, and general tools. Most tools are made of wood just like in the middle ages of Europe.
The dwarves have the secret of making good steel and cheaper iron via blast furnaces. All other races that use iron have to use bloomeries, although they use sea shells to remove the impurities from the ore. As such, the carbon content of non-dwarven iron materials is variable,and often not usable for weapons. Many places have trouble making iron that is good enough for basic tools even. Most islands will roast ore, and run it through a bloomery to produce pig iron. They then ship the pig iron to dwarven cities for further refining and working.
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Stone and ceramics are in common use. The dwarves are also noted for their stone work. Many of the items that are made with large amounts of metal on Earth are made of stone or ceramics on Oceana. This includes high efficiency fire places & ovens, cooking pots, frying pans and such. Concrete and cement are known from Roman days, but are not much used. The energy needed to make both of them mitigates the wide spread use of either concrete or cement. They have the kick pottery wheel.
Wood is in common use for many things. The protection of forests is a religious duty though. There are religious restrictions on cutting down trees. The restrictions are to ensure a permanent growth of forests while providing wood for the various races. Deforestation was an issue historically, but has been solved in most civilized city-states for the past 1,000 years. Bamboo is in common usage since it is fast growing. It is used for furniture, building and fuel.
Glass production is expensive but does exist. Glass production competes with metal working for any type fuel, and to a different extent with shipbuilding for older trees. There is no plate or flat window type glass.
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Oceana has the spinning wheel, cotten gin and loom. The larger city-states have wind powered and water powered fabric mills on the order of early 19th century England. There is an active trade of raw wool, cotten, flax and similar between smaller agricultureal islands and these production islands. The technology is widely known to specialists, but is fairly expensive in terms of capital costs.
Most cloth production is only slightly above the originial Roman era. Women still do the spinning, but instead of the distaff or drop spindle, they have the spinning wheel. Greece, Rome and more northern areas are major producers of wool and flax. Cotton and silk are an Egyption monopoly.
Medicine is fairly primitive in most of Oceana. The existance of magical cures has held back the need or desire to improve things. Surgery is fairly common, and the cure disease spell has made survival reasonable.
Roman numbers were in use until 100 CE. There was no zero. This kept math, accounting, and general science theory at a fairly low level for a very long time. The Greeks were the closest thing to scientist on Oceana. Egpyt is not known for theoretical knowledge or experimantation.
Until recently the Oceana economy was fairly simple. Despite the on going ocean trade, there was no banking or credit system. The limited liability corporation has to be common. Most of Oceana's major powers are still cash economies though.. Taxes are paid in cash, instead of the feudal method of crops and goods.
Unlike the late Roman Empire, the economy is not moribound. Land is not owned by just a few people with huge estates. Slaves are not the normal field workers, in Greek settled areas.