GZDoom is a feature centric port for all Doom engine games
The Ren'Py Visual Novel Engine
s&box is a modern game engine, built on Valve's Source 2
UZDoom is a feature centric port for all Doom engine games
05k0nz's legacy is safe
A free/open source client and automation tool for Ragnarok Online
Experimental menu for GTA 5: Enhanced
Cross-platform, open source, and super fast MUD client with scripting
Complete Open Source and Modular solution for MMO
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
Skript is a Bukkit plugin which allows server admins
Cross-platform 2D and 3D game engine with modular architecture
A free mixin-based injection hacked client for Minecraft
An updated version of the classic "Basic Computer Games" book
Stride (formerly Xenko), a free and open-source cross-platform C# game
Free game engine for development of desktop, mobile, and web games
A completely free, open-source, 2D game engine
Multi Theft Auto is a game engine
Games you can play in your terminal written in go
Cocos simplifies game creation and distribution with Cocos Creator
3D Game engine with editor
Python MUD/MUX/MUSH/MU* development system
Cross-Platform C++ 2D/3D game engine
Voxel game-creation platform with easy modding and game creation
An OpenGL RTS game engine written in C