Mesa.
Non-OpenGL API renders:
-
https://github.com/ssloy/tinyrenderer, renders: https://en.wikipedia.org/wiki/Wavefront_.obj_file files.
Integrated into the Bullet Physics viewer: https://www.youtube.com/watch?v=Lz08cFuE1Q0, and you can switch on the fly between OpenGL and tiny-renderer.
TODO: OpenCL implementation?!