The Ren'Py Visual Novel Engine
Fast and lightweight JavaScript game engine built on WebGL and glTF
3D game engine/framework in C, with Luajit and Python bindings now
A completely free, open-source, 2D game engine
3D Game engine with editor
A dead simple 2D game engine for Go
High performance UI layout library in C
Zig game engine & graphics toolkit
Starter project to get a Phaser game environment up and running
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3