I guess free is kind of with an asterix here, as Sonic and All-Stars Racing Transformed is free this weekend on Steam, at least to try, until Sunday at 1pm Pacific, when it will require you to actually purchase the game to continue playing it. Think of it as a multi-day full demo of a game that allows you to explore every nook and cranny of it and figure out if you want it or not. Sonic and All-Stars Racing Transformed is also heavily discounted this weekend, as well, so if you like it you should probably fork over those ducats for it, as it is 75% off, which means $7.49 USD.
Sonic and All-Stars Racing Transformed is a pretty crazy kart racing game with that special SEGA and Sonic touch to it. Your car will not only travel on land, but will transform into a plane or a boat depending on the landscape in the certain track. That is where the “transformed” part comes in. If you buy it on Steam there are also some extra characters, as well, from Team Fortress Classic 2 and Company of Heroes 2.