Frogatto

Those who enjoy a good 2D Mario or Sonic game will definitely like Frogatto. A little cutesy for my taste, but it's a well done platformer. It's available for Windows and Mac (free) as well as iPhone and iPad ($5 not so free) and the source code is available as well. The company plans to expand on the game due in part to it's success on the Apple store but being an open source project you can expect fan made freebies as well.