Flight is an upcoming1 open source aerial combat game built on OpenGL. It features procedurally generated content, and smooth cel shaded graphics.
1 I was developing the game on a mac, and Apple is dropping OpenGL, so I've decided not to continue this project.
If you're running macOS everything should go fairly smoothly. Otherwise, you may need to add a few lines to the CMake script in build/ according to your platform (this would be a great way to contribute).
cd build/
cmake .
cd ../deps/
# Compile each dependency
cd ../build/
make
Note: I believe there's a race-condition on the linux builds for which I need to add some more locks. I saw the error where XLib complains that you didn't call XInitThreads, which is never the real problem, almost always a synchronization thing.