I think Joe's Monsterhearts is damn near playable, he's planning on putting out the last bit of required playtest info soon.
And "Rogue Trader Apocalypse" has apparently been a play in progress kind of thing.
Also, I think that Sagas of the Icelanders is playable.
Oh, and of course, Dungeon World has been playable for awhile.
Hopefully one of those sounds interesting :)