GitHub is a goldmine of resources for game developers. I'd like to introduce you to five open source projects that'll help you build your first, or next, amazing game. Check them out for your weekend projects, Game Jam entries, or day-to-day projects at work!
Introducing Torque 3D, Spring, Flixel, Three.js, and cocos2D...
Torque 3D was recently open sourced by Garage Games along with several templates and tutorials to help you build 3D games for the Windows, Mac, Linux, XBOX 360, or Wii platforms. It comes with an impressive world-editing suite, and a ton of other features. It's open source, extremely customizable, and extendable through Torquescript.
If you've used it in the past and/or are interesting in joining the Torque 3D open source steering committee, please take a look at the membership charter (draft).
Flixel is a great little library that is free for personal or commercial use and is easy to learn, extend, and customize. It was created by Adam "Atomic" Saltsman and written entirely in ActionScript. It's packed with some amazing features - all well-documented with examples and with source code readily available.
You might recognize one of these games that Adam created - Canabalt (a personal favorite of mine), Mode, Gravity Hook, and Fathom.
There are a number of web-based games and demos you can see that use it (fair warning - expect to be lost playing/experimenting with these for the next couple of hours):
Spring is a 3D RTS game engine developed for Windows and Linux with experimental Mac support. It started out with the intention of bringing the gameplay experience of Total Annihilation into 3D. They have some excellent documentation to help you get started.
Have you used any of these projects in a school project or Game Jam? We'd love to hear about it - email us at email@example.com.