Xash3D FWGS engine
Godot is a powerful cross-platform game engine
A complete 3-D game development suite written in Java
Cross-platform 2D and 3D game engine with modular architecture
Cross-Platform C++ 2D/3D game engine
Voxel game-creation platform with easy modding and game creation
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
The Ren'Py Visual Novel Engine
Stride (formerly Xenko), a free and open-source cross-platform C# game
Cocos simplifies game creation and distribution with Cocos Creator
Recreation of the classic Grand Theft Auto III game executable
Powerful, mature open-source cross-platform game engine for Python
Free game engine for development of desktop, mobile, and web games
Free, cross-platform 2D game engine powered by Haxe and OpenFL
The HTML5 Creation Engine
The ioquake3 community effort to continue supporting/developing id's
Voxel game engine in C++ with OpenGL
Zig game engine & graphics toolkit
Cross-platform 2D game engine focused on ultimate productivity
Descent 3 by Outrage Entertainment
A game engine powered by python and panda3d
Open source library for creative expression on the web, desktop, etc.
The game engine for everyone
Cross-platform game engine in Rust
3D Procedural Game Engine Using OpenGL