This year, quite a few interesting FOSS game projects got accepted (again) and one being our very own friends of the SuperTuxKart project.
Read more about their role as a mentoring organization here. So how about applying as a participant yourself and helping out this great FOSS game?
You can also browse other accepted mentoring projects here, if SuperTuxKart isn't your thing. Other notable FOSS game (engine) projects accepted are:
Nice summer of coding ahead :)