Source of Mana is a unique 2D MMORPG
You can make it - Open Source MMORPG Platform
Open QR Code is an open-source, cross-platform app
State-of-the-art 2D and 3D Face Analysis Project
Open Source MMORPG Framework
A web-based IDE for HTML5 game development. Powered by Phaser
Classic 2D side-scrolling platformer game
Pencil2D is an easy, intuitive tool to make 2D hand-drawn animations
Free, cross-platform 2D game engine powered by Haxe and OpenFL
LÖVE is an awesome 2D game framework for Lua
Cross-Platform C++ 2D/3D game engine
Cross-platform 2D game engine focused on ultimate productivity
Pymunk is a easy-to-use pythonic 2d physics library
LayaAir is an open-source 2D/3D engine
2D JavaScript Physics Engine
Juggling Lab juggling animator
A J2ME emulator for Android
A 2D rigid body physics engine for the web
OpenSoldat is a unique 2D (side-view) multiplayer action game
A Vulkan and OpenGL overlay for monitoring FPS, temperatures, CPU/GPU
Cross-platform 2D and 3D game engine with modular architecture
2D GPU-accelerated framework for ActionScript developers
Phaser is a free and fast 2D game framework for making HTML5 games