UPDATE April 26, 2008: D6 MOD 7 is no longer being actively developed. Feel free to use the mechanic for anything you'd like. It would be nice to attribute the idea to me, but that is not necessary. I'd rather have the material available to you rather than concern about contacting me for permission.
As an alternative to other mechanics in role playing games, the player characters are given a slight advantage based on dice rolls instead of higher attributes.
The mechanic is:
Roll three standard dice and total the result. Divide by the largest factor of 7 and use the remainder (or modulus).
All non-player characters roll two standard dice instead of three. Otherwise, their roll is also computed by totaling the result and finding the modulus 7.
The advantage is approx 5.5% on average in favor of player characters.
It is much easier than it may sound. Once you do it a few times, it becomes second nature. However, Dice Sheets are provided if you do not wish to go through the computation.