GURPS

Generic Universal Roleplaying System - created by Steve Jackson

GURPS is just another role playing system. The real advantage to the GURPS concept is that it allows you to move from one type of game to another. I've played a western/cthulu game in GURPS and lots of superhero games, street level fighting in any era is possible without having to learn new rules. That's the beauty.

The website will tell you pretty much all you want to know about it.

I am not currently in a GURPS campaign