GURPS, which stands for Generic Universal Role Playing System, is a second-generation RPG system. It broke the class-and-level mold of the earliest games and presented instead a point-based character construction system where each attribute and skill was purchased separately, allowing players to create a character in fine detail.
It uses a 3d6 roll-under mechanic for practically everything except damage. The system is designed to be genre-agnostic, freeing players from the need to learn a new system every time they want to change genres.
Currently GURPS is published in its fourth edition(4e). It is a product of Steve Jackson Games. More information can be found at http://www.sjgames.com/