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. Before GURPS, Steve Jackson wrote a set of games called The Fantasy Trip, which are strongly related to GURPS.

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. Most other role-playing systems generate character characteristics using dice.

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/.