The Summit Engine is a game engine for 2D adventure-action role playing games.
It is written in C++, uses the Boost Library as well as the Simple Direct Media Layer.
It runs on Windows and Linux natively; it should run on most other systems, even though they have not been tested yet.
The engine itself is under the MPL; you're allowed to put all your game resources (sprites, sounds, etc.) under the license you wish though.
The examples provided with the engine are under the Creative Commons by-sa license.