Simple 20 is a generic game system inspired by d20 and BRP. It is simple in design, uses minimal rules and is easily adapted to any genre of gaming with a minimum of effort (depending on the level of detail desired).
These rules are the evolutionary descendant of James Hargrove's earlier Core Elements[/rpg]. These rules seem a little tighter and more distilled than in Core Elements[/rpg].
designer's notes from rules postscript"
This set of rules was inspired by several pre-existing works, including the World's Most Popular Roleplaying Game (now in its third edition), the World's Most Popular Percentile-Based Roleplaying Game (recently released under the OGL), Core Elements, and Scott Lininger's The Window (no kidding).