Multi Theft Auto is a game engine
Xash3D FWGS engine
fheroes2 is a recreation of Heroes of Might and Magic II game engine
Descent 3 by Outrage Entertainment
The game engine for everyone
Open-source engine for Heroes of Might and Magic III
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
Voxel game-creation platform with easy modding and game creation
Go bindings for raylib, a simple and easy-to-use library
Cocos simplifies game creation and distribution with Cocos Creator
Stride (formerly Xenko), a free and open-source cross-platform C# game
Open source clone of the Age of Empires II engine
Multi-platform 2D and 3D game engine
Free game engine for development of desktop, mobile, and web games
Solar2D Game Engine main repository (ex Corona SDK)
The flexible game engine
Voxel game engine in C++ with OpenGL
RPG Maker 2000/2003 and EasyRPG games interpreter
A pure Go game engine
Cross-Platform C++ 2D/3D game engine
3D game engine/framework in C, with Luajit and Python bindings now
Powerful, mature open-source cross-platform game engine for Python
An OpenGL RTS game engine written in C
Svelto ECS C# Entity Component System
Cross-platform 2D game engine focused on ultimate productivity