The latest Humble Bundle offering is a Bohemia Interactive special, full of their military sim Arma titles (and a few spin-offs). Standard rules apply; you pay (pretty much) what you want, and are rewarded with games accordingly.
At the ‘$1 or more’ level, that means the original Arma (Gold Edition), Cold War Assault, and the turn-based title Tactics. Step it up to beating the average amount (currently a touch over $10), and you can add Arma 2 and all of its expansions to that haul. At the $15 mark, you get all of the above plus Arma 3 and, the greatest prize of all, the karting spin-off Karts.
The designated charity for this one is the American Red Cross, and as usual you can split your payment however you choose between charity, Bohemia themselves, and Humble Bundle.