Voxel game engine in C++ with OpenGL
3D game engine/framework in C, with Luajit and Python bindings now
High performance UI layout library in C
Zig game engine & graphics toolkit
Here we're trying to create the easiest open-source game engine.
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
Educational framework for OpenGLES, OpenCL and OpenAL