Pygame!

Orx - a portable open source game engine

Script runtime for rapid software development.

Cross-platform windowing and multimedia library for Python.

thinBasic is a simple, flexible, and easy-to-learn interpreted programming language. It lets you quickly and easily develop programs for Windows. thinBasic was first released in 2004. Since then thinBasic has steadily improved thanks also to the help of a growing number of enthusiastic users. Although thinBasic is an interpreted language providing subscript checking, un-initialized variable checking and numerous other run-time checks, it is extremely fast. People use it to develop Windows GUI programs, high-speed OpenGl games, Windows programs (GUI or Console), task automations. It is also very useful for CGI (Web-based) programming. »

Flixel is and open source game-making library in ActionScript3. Designed for use with free tools Flixel is easy to learn, extend and customize.

Build games and applications for almost every platform imaginable -- Windows, Mac, Linux, iOS, Android, BlackBerry, Firefox OS, Tizen, Flash and even HTML5. Bring your creative vision to life, on desktops, tablets, phones, even consoles. Publish to Steam, Amazon, OUYA... practically anywhere.

A platform independent 2d game programming framework for c/c++ programmers with least possible dependencies for easy porting and with focus on easy API calls and the requirement of commercial programmers.

sdlBasic is a small, efficient and multiplatform basic interpreter aimed to game creation using the power of SDL library, it was inspired by the old and glorious AMOS.sdlBasic is open source software. This means anyone is welcome to download it at no charge, including the source code if you need to make special changes.

HaxeFlixel is a 2D Game Engine that lets you create cross-platform games easier with free, open source technology!

FlashPunk is a free ActionScript 3 library designed for developing 2D Flash games. It provides you with a fast, clean framework to prototype and develop your games in. This means that most of the dirty work is already done, letting you concentrate on the design and testing of your game.

Monkey is a modular language. You can create your own custom modules and use other people's - including the awesome box2d and minib3d modules!

Arianne is a multiplayer online games framework and engine to develop turn based and real time games. It provides a simple way of creating games on a portable and robust server architecture. The server is coded in Java and you may use Python for your game description, provides a MySQL or H2 database backend and uses an TCP transport channel to communicate with hundreds of players.

HGE is an easy to use yet powerful hardware accelerated 2D game engine. It is a full featured middleware for all who want to develop commercial quality 2D games rapidly and easily. It covers all imaginable 2D game genres: you could create everything from a simple puzzle to advanced multilayered platformer or strategy without even thinking of any non game logic code! And you don't have to know anything about "window messages", DirectX programming and all that stuff. Instead you can start developing your own game within 15 minutes! »