Second System is an upcoming, ameteur, and most-likely-vapourware FOSS game designed by a bored /g/entooman...
Still interested? Second System is styled to take a different turn from the modern direction, offering a throwback to DnD games of yore - encouraging lore and socialising over mindless slaughter and canned plots. Sounds a lot like the usual marketing, eh? This time, however, it's true. Using a server backend of CommonLISP, the game is designed to evolve not only it's content, but the very code itself: imagine a magic system that allowed you to program spells, or a world that gains depth by itself.
It's surprisingly easy actually, I'm surprised none's done it before.