Since some of you may have stumbled across this without the benefit of the thread that started it, here's a quick n' dirty pitch for Wizard World:
Wizard World is an attempt meld the complex conceptual brilliance of Ars Magica with the simple elegance of the Apocalypse Engine. In addition to the individual characters, the group shares a character in the form of the covenant, or home base.
You can also check out the original thread here:
http://apocalypse-world.com/forums/index.php?topic=6646.0