Phaser is a free and fast 2D game framework for making HTML5 games
Framework to facilitate communication in the Unity game engine
Godot game template and component-based framework
3D game engine/framework in C, with Luajit and Python bindings now
Arianne is an engine to develop multiplayer online games like Stendhal
Open-source full-stack web development framework built on top of React
Easily generate thousands of 3D models, images, and animation NFTs
A Rust framework for building Minecraft servers
Plugin pack for making 2D games with Bevy
A complete framework for Godot to create beautiful and complex AI
Open-source, cross-platform, game-development tools
Build Cross-platform Applications
MMORPG
Game engine allows you to create own MMORPG
3D .NET engine for Windows, Linux, Mac
A Flash Molehill (Stage3D) GPU accelerated 2D game engine
The Flixel Power Tools are a set of plug-ins for Flixel 2.5+
Cross platform 2D game creation framework with Python bindings
Formerly CraveJs, it's for creating JavaScript applications and games.