Godot is a powerful cross-platform game engine
Multi Theft Auto is a game engine
A game engine powered by python and panda3d
The Ren'Py Visual Novel Engine
Xash3D FWGS engine
Open-source engine for Heroes of Might and Magic III
Real Time Strategy game engine supporting early Westwood classics
The game engine for everyone
Voxel game-creation platform with easy modding and game creation
A complete 3-D game development suite written in Java
fheroes2 is a recreation of Heroes of Might and Magic II game engine
Open source voxel game engine with support for survival and crafting
dhewm 3 main repository
A retro game engine for Python
A modular Common Lisp game engine
Cocos simplifies game creation and distribution with Cocos Creator
Fast and lightweight JavaScript game engine built on WebGL and glTF
The ioquake3 community effort to continue supporting/developing id's
A refreshingly simple data-driven game engine built in Rust
Open source clone of the Age of Empires II engine
Magic Another Game Engine
Voxel game engine in C++ with OpenGL
A 2D rigid body physics engine for the web
Descent 3 by Outrage Entertainment
Solar2D Game Engine main repository (ex Corona SDK)