The miniature car racer 'OverVolt: crazy slot cars', is a favorite Windows Phone game of ours. For the next week, it's an even bigger favorite, due to the premium pack for the game being offered for free this week.
While OverVolt is free on its own, its premium pack normally costs $2.49 via an in-app purchase. It offers players access to unlimited online multiplayer matches versus just three matches per day without the pack. It also adds 5,000 in-game credits, and a way to save personalized car textures.
It doesn't hurt that the main game is a ton of fun to play, as you pilot miniature slot cars over 30 different tracks. Making the premium pack free makes it an even better value.
Source: OverVolt (Twitter)