You can make it - Open Source MMORPG Platform
Godot is a powerful cross-platform game engine
A simple and easy-to-use library to enjoy videogames programming
Enables Roblox developers to use professional software tools
Desktop/Android/HTML5/iOS Java game development framework
Open Source MMORPG Framework
One framework for creating powerful cross-platform games
Self-hosted CMS platform based on the Laravel PHP Framework
Real Time Strategy game engine supporting early Westwood classics
Open source HTML5 game framework that offers WebGL and Canvas
A game framework written with osu! in mind.
Gideros Release version
Open source library for N64 development
Open source library for creative expression on the web, desktop, etc.
All-In-One program that combines multiple Fortnite Dev Account tools.
Examples of procedural geometry for Unity3D C#
PyCAPGE - Python Classic Adventure Point and Click Game Engine
Game engine supporting many 3D/2D formats and graphic effects
INSTEAD - Simple Text Adventure Interpreter.
JavaScript framework to build game engines, games, emulators and apps
2D Game Engine
A real-time game development platform
A cross platform Lua based game engine
Cross-platform 2D and 3D game engine
Example code for creating a 2D platform game in Java.