Reaktor
Developed in 2004, with my brother-in-arms Tiago "Azorian" Rodrigues, this was our way of completing a Computer Graphics assignment in college.
We neede to show what we learned about OpenGL, and what better way to do that than to implement a first person shooter game engine prototype from scratch featuring a physics engine, networked multiplayer mode, quake map loading (we were able to edit the maps in QuArK), BSP partitioning.
Like good linux fans, we supported both Win32 and linux versions.
If I recall correctly, we used MingW as the compiler (a windows native gcc port), and the ever popular GVim as text editor / IDE.
Apart from OpenGL, we used SDL for interacting with the OS and OpenAL for sound.