Godot Minimal Theme
Multi-platform 2D and 3D game engine
The ioquake3 community effort to continue supporting/developing id's
Solar2D Game Engine main repository (ex Corona SDK)
An OpenGL RTS game engine written in C
Full featured MUD server with all the trimmings.
Rust library to create a Good Game Easily
Retro game engine for creating games like it's 1997
Improved version of the X-Ray Engine, the game engine
KlayGE is a cross-platform open source game engine
A 2D game engine base on OpenGL and SDL,support for Windows & Linux
Turn Based Game Engine (GMS GML)
Cross-platform 2D game engine