A Modular, Open-Source Roleplaying Game
From the introduction:
Welcome to Modos! Modos RPG is a modular, open-source, roleplaying game designed for fast play, roleplaying flexibility, and simplicity. The rules were written first in outline form, so that anyone playing it could add or subtract rules as desired. This is what's meant by open-source. Further, the game's simplicity allows it to take on new personalities by adding sets of rules or adventures. This is why it's called modular. The end result is, hopefully, the roleplaying game that perfectly meets your needs.