I think everyone has heard of the first one - if you haven't: You get a bunch of games that are completely DRM-free and work on Linux, Mac OS and Windows. You pay as much (or as little) as you want to, and can also decide where you want the funds to go (to the developers, to charity, or both). The following titles are included: Braid Cortex Command Machinarium Osmos Revenge of the Titans Available at www.humblebundle.com. Nobody should be without a copy of Braid imo, and Osmos makes it a great gift choice for your casual gamer friends too.
I got an email about Humble Bundle 1 the other day - a Steam code i could use to add the games I bought to my Steam account. Very nice!
