CGL (C Game Library) is a multipurpose library
An implementation of OpenGL 3.x-ish in clean C
Retro Computer Image Library
SDL based generic 2D game engine
A 16 bit style game on the 16-bit IBM XT.
BASIC for the modern era
The penultimate portable graphics library
Low-Level Game Engine for Retro Platforms
A C Compiler/Editor for Retro 6809 Machines (Colour Computer/Dragon)
Twin is a "retro" program for embedded or remote systems