UCI chess engine
Xash3D FWGS engine
RetroArch is a frontend for emulators, game engines and media players.
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
A MUD client for Android, iOS, Linux, Mac OS X and Windows
Orx: Data-Driven Game Engine
GameServer is a sophisticated, game server designed for online games
Free idle clicker themed around cthulhu
A 2D game about Bunny and coronavirus
Character animation system for games and simulations.
God game: wage war from the stone age to the future
Real-time RPG for PC/tablet/phone; multiple quests and random dungeons
Asphyre is a cross-platform framework for Delphi and FreePascal.
online 4X browser game engine
Remake of the classic Caesar III game
3D .NET engine for Windows, Linux, Mac
Small Java game such as "Connect Four" but something differently.
Science Fiction, heavy assault, disestablishment of power.
An Action Adventure Space Physics Game
A D20 combat initiative tracker