Humble Store is now celebrating its third anniversary with a birthday sale with savings on a bunch of games. There is also a freebie, as they now offer DiRT 3 Complete Edition for Windows and OS X completely free, which our calculations show to be more than half off. This is part of their birthday celebration and while the game will be yours to keep, you must pick up your copy before the timer hits zero, under 48 hours from now. The complete edition comes with seven content packs along with the base game and full Steamworks integration, so a Steam key is required. Here's an overview:

Get DiRT 3 Complete Edition, the definitive edition of off-road racer DiRT 3 now expanded with extra content and enhanced with Steamworks integration, including Achievements, Leaderboards and Steam Cloud Saves.

In DiRT 3 Complete Edition, you’ll race iconic cars representing 50 years of off-road motorsport across three continents – from the forests of Michigan to the infamous roads of Finland and the national parks of Kenya. You’ll also express yourself in the stunning Gymkhana mode, inspired by Ken Block’s incredible freestyle driving event, and take on other modes including Rallycross, Trailblazer and Landrush. Powered by Codemasters’ award-winning EGO Engine, DiRT 3 Complete Edition features Flashback to rewind time, genre-leading damage and you can take on all game modes in split-screen and competitive online multiplayer.