The Humble Weekly sale this week is for three games from Klei Entertainment. You can get Shank, Shank 2 and Eets for just $1.
All games are for Mac, PC and Linux except for Eets which does not have support for Linux. All three games come with Steam keys.
The price is in US dollars and excludes any tax. Money spent can be divided between the developers of the game and charity at any ratio you want.