So hey! Today is Free RPG Day! It’s a little less popularized than Free Comic Book Day, but hey, rolling dice isn’t for everyone.
For my part, I shall offer the following:
GURPS Lite: http://www.sjgames.com/gurps/lite/ - I prefer the third edition rules, and the Lite version actually has a couple of spells for a fantasy game.
Risus: http://www222.pair.com/sjohn/risus.htm - Very rules-light, bordering on beer’n'pretzels. Geared for slightly silly one-shots, it can be played as a serious campaign, too.