s&box is a modern game engine, built on Valve's Source 2
The Ren'Py Visual Novel Engine
Cross-platform 2D and 3D game engine with modular architecture
Complete Open Source and Modular solution for MMO
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
Stride (formerly Xenko), a free and open-source cross-platform C# game
Free game engine for development of desktop, mobile, and web games
3D Game engine with editor
Cross-Platform C++ 2D/3D game engine
Skript is a Bukkit plugin which allows server admins
Experimental menu for GTA 5: Enhanced
Cocos simplifies game creation and distribution with Cocos Creator
A Bee Swarm Simulator macro for Windows
Cross-platform, open source, and super fast MUD client with scripting
Stipple Effect is a pixel art editor that supports animation
Games for tomorrow's programmers
Multi Theft Auto is a game engine
A Fantasy Console intended as a tool for pixel art game development
A completely free, open-source, 2D game engine
A free mixin-based injection hacked client for Minecraft
A free/open source client and automation tool for Ragnarok Online
Kitty-Tools is a Kahoot Cheating Client for all devices and interfaces
Voxel game-creation platform with easy modding and game creation
Flax Engine, multi-platform 3D game engine
An OpenGL RTS game engine written in C