Gears

From Introduction:

Gears is a free role playing game system that was created with the busy GM in mind. You don't have to read a book with the size of the NY phone book before you can start playing. Character creation takes only a few minutes and after that you can start playing in almost any genre.

Gears uses regular six-sided dice. Usually you have to roll several dice, sum up the results and add a modifier. As a shorthand we usually use something like that: 3d6+2. This means, you have to roll three dice, sum up the result and add 2.