Godot is a powerful cross-platform game engine
Xash3D FWGS engine
Injectable LUA scripting system, SDK generator, live property editor
Multi Theft Auto is a game engine
Open source voxel game engine with support for survival and crafting
Fast and lightweight JavaScript game engine built on WebGL and glTF
Solar2D Game Engine main repository (ex Corona SDK)
The Ren'Py Visual Novel Engine
A game engine powered by python and panda3d
A complete 3-D game development suite written in Java
Real Time Strategy game engine supporting early Westwood classics
fheroes2 is a recreation of Heroes of Might and Magic II game engine
Voxel game-creation platform with easy modding and game creation
Recreation of the classic Grand Theft Auto III game executable
The ioquake3 community effort to continue supporting/developing id's
The game engine for everyone
Open-source engine for Heroes of Might and Magic III
Open source clone of the Age of Empires II engine
Powerful, mature open-source cross-platform game engine for Python
Free game engine for development of desktop, mobile, and web games
RPG Maker 2000/2003 and EasyRPG games interpreter
Multi-platform 2D and 3D game engine
Magic Another Game Engine
Stride (formerly Xenko), a free and open-source cross-platform C# game
Cocos simplifies game creation and distribution with Cocos Creator