Godot is a powerful cross-platform game engine
Multi Theft Auto is a game engine
Voxel game-creation platform with easy modding and game creation
Open 3D Engine (O3DE) is an Apache 2.0-licensed multi-platform 3D
The ioquake3 community effort to continue supporting/developing id's
The Ren'Py Visual Novel Engine
Open source clone of the Age of Empires II engine
Recreation of the classic Grand Theft Auto III game executable
Powerful, mature open-source cross-platform game engine for Python
Open source library for creative expression on the web, desktop, etc.
Multi-platform 2D and 3D game engine
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
Cross-platform 2D game engine focused on ultimate productivity
A game engine with an emphasis on real-time cutting-edge solutions
Zig game engine & graphics toolkit
A Flutter based game engine
A fresh & lightweight javascript game engine
Descent 3 by Outrage Entertainment
A 2D rigid body physics engine for the web
Modified source engine (2017) developed by valve and leaked in 2020
MIT Licensed Open Source version of Torque3D from GarageGames
Retro game engine for creating games like it's 1997
3D C++ Game Engine - yet another open source game engine
An open source re-implementation of Diablo 2