Orx: Data-Driven Game Engine
RPG dice roll simulator for vintage Tandy TRS-80 100/102/200 laptops
Low-Level Game Engine for Retro Platforms
Multi-platform game engine similar to old Megaman with a stage editor
A generic 2D engine for any kind of game
TurboSphere is an easy to learn and powerful JS based game engine.
A Simple Game Engine
a flexible game engine
Reference implementation for the Doom game engine.