The Category Menu

...contains Name Category, Insert/Insert Multiple, Delete/Destroy, Add to/Remove from Outbox as Category, Add this cat's notes to Outbox, and Remove this cat's notes from Outbox.

Name Category allows you to name -- or rename, as appropriate -- the current category.

Insert will insert a new blank category column at the current position, shoving categories rightward as necessary. Hold the Shift key down while clicking the Category menu item and Insert will become Insert multiple, should you happen to want more than one. There's a current limit of 1,000 categories.

The next item will appear either as Destroy (if the category has at least one note) or Delete (if it doesn't). There is as yet no Undo available, so be careful. (See, there IS a reason for File|Mark As Unchanged.)

Add to Outbox as Category will add the category to the outbox, while Add this cat's notes to Outbox will add all the notes in the category to the outbox. Adding the category as a category is how you currently extract an arbitrary selection of categories to a new notebox file, in conjunction with the File|Export Outbox function. (Individual notes will be exported as a new, seperate category. Hmm, now what happens if you have 1,000 categories, export all of them as categories, AND select notes individually? Smells like a bug...) If the category is already in the Outbox, "Add to" will become "Remove from", so that you may do so. Remove this cat's notes from Outbox will remove any individually-added notes in the category from the outbox.