I’ve been working on a puzzle game which targets libretro lately: http://forums.tigsource.com/index.php?topic=31218.0
It’s written in C++11 and we have builds running on Linux, Windows, Android and Pi atm. It’s currently in a test phase, so the source of the libretro core isn’t opened yet. It will be when it’s done, however.
There’s also a very simple launcher for it written in Qt. Downloads can be found in the tigsource thread.