Xash3D FWGS engine
The Ren'Py Visual Novel Engine
The ioquake3 community effort to continue supporting/developing id's
RPG Maker 2000/2003 and EasyRPG games interpreter
Open source voxel game engine with support for survival and crafting
Cross-Platform C++ 2D/3D game engine
Cocos simplifies game creation and distribution with Cocos Creator
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
dhewm 3 main repository
Real Time Strategy game engine supporting early Westwood classics
Descent 3 by Outrage Entertainment
Cross-platform 2D and 3D game engine with modular architecture
fheroes2 is a recreation of Heroes of Might and Magic II game engine
A completely free, open-source, 2D game engine
Multi Theft Auto is a game engine
Open-source engine for Heroes of Might and Magic III
Free, cross-platform 2D game engine powered by Haxe and OpenFL
Stride (formerly Xenko), a free and open-source cross-platform C# game
Open game and rendering engine packed into a JavaScript framework
Voxel game-creation platform with easy modding and game creation
Free game engine for development of desktop, mobile, and web games
A .NET ascii/ansi console engine written in C# for MonoGame and XNA
Cross-platform 2D game engine focused on ultimate productivity
3D game engine/framework in C, with Luajit and Python bindings now
Voxel game engine in C++ with OpenGL