Just saw this on Slashdot Games: Three Rings Design , makers of Yohoho! Puzzle Pirates has just released open source versions of their game-making toolkits at http://www.gamegardens.com/. (Yes, this sentence needs more hyperlinks, I know.)
Anyway, I haven’t looked at it in depth, but the concept is pretty cool. Assuming that you have most of the technical bits needed to make a game, this is a good thing. Looks like they’re even providing free hosting for games.
It’s also noteworthy that PopCap, makers of that timestealer Bejeweled, released their own framework for making games. Again, a great step towards helping games get developed.
And since I’m mentioning everyone, I recommend that people check out GarageGames and the cool Torque engine. For people that need a great graphics engine for their genre-defying future projects.