GURPS

A very modular and customizable pencil and paper role-playing game system. GURPS stands for Generic Universal Role Playing System. It can be used to play games in fantasy, modern, futuristic, or historical settings.

GURPS is a product of Steve Jackson Games.

Together with the [Hero system]?, GURPS was one of the first role-playing games in which characters are created by spending points to get characteristics, skills, advantages, getting more point by accepting low characteristics, disadvantages etc.

The main game mechanics consists in rolling 3 six-sided dice, and having to roll as low as possible, and in any case lower than the skill or characteristic concerned.

You can get a printable PDF version of the "lite" rulebook for free at http://www.sjgames.com/gurps/lite/.