The Omni system is a rules lite universal RPG.
It is basically the blood and guts of the more familiar title Talislanta.
All tests [combat, social, academic] are resolved with a single roll of a d20. D&D 3.0 and the d20 System have borrowed heavily from the concepts pioneered by Talislanta.
It is supremely flexible and allows for exciting dramatic risk but is simple enough to fade into the background and allow players and GMs alike to focus on collaborative storytelling.