Various things for PSX (PlayStation 1, PSone)
Open 3D Engine (O3DE) is an Apache 2.0-licensed multi-platform 3D
Cocos simplifies game creation and distribution with Cocos Creator
Voxel game engine in C++ with OpenGL
Cross-Platform C++ 2D/3D game engine
UZDoom is a feature centric port for all Doom engine games
Cross-platform 2D and 3D game engine with modular architecture
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Stride (formerly Xenko), a free and open-source cross-platform C# game
Java/JavaFX/Kotlin Game Library (Engine)
DeSmuME is a Nintendo DS emulator
Open source library for creative expression on the web, desktop, etc.
A Minecraft mapping tool that creates 3D models of your Minecraft
A modular Common Lisp game engine
Xash3D FWGS engine
Multi-platform 2D and 3D game engine
Zig game engine & graphics toolkit
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
OptiScaler bridges upscaling/frame gen across GPUs
3D and 2D game engine written in Rust
One framework for creating powerful cross-platform games
Cross-platform game engine in Rust
3D game engine/framework in C, with Luajit and Python bindings now
Powerful, mature open-source cross-platform game engine for Python