Cocos2d is an open source 2d game engine using C++. I've never used it but it's fairly popular http://www.cocos2d-x.org/cocos2dx. Monogame would be a good choice for a 2d game in C# http://www.monogame.net. I'm not familiar with any engines in C, but this list might help you https://en.m.wikipedia.org/wiki/List_of_game_engines. Best of luck!