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