DirectToTheFingScreen
A low-level 3D software renderer that writes directly to the Linux framebuffer with no external graphics libraries.
No OpenGL, no Vulkan, no SDL — this writes pixels straight to /dev/fb0. The whole transformation pipeline (model space through to screen space) is hand-rolled, which meant relearning matrix math the hard way instead of trusting a library to do it right.
Runs on any Debian-based distro with the desktop environment disabled, which is a good way to find out how much a compositor was doing for you.