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