Spring

Spring is a 3D RTS engine that is entirely licensed under the GPL. It is written in the C++ programming language and uses the SDL/OpenGL and OpenAL API, Games are written entirely in lua.

Most of these games and their content are under free licenses.

Features

 * Massive battles with up to 10000 units on large maps
 * Land, Sea and Air battles
 * Shields, superweapons, and weapons of mass-destruction
 * Full featured 3D graphics
 * Zoom out to get an overview of the whole map
 * The ability to follow individual units with close-up
 * Flexible user's lua widgets system, including pixel-shading, UI and unit behaviour tweaks
 * Huge variety of games
 * Lots of different maps available

Minimum System requirements

 * OpenGL 3.0 capable video card
 * Pentium 4, Athlon XP or higher CPU
 * 512 MB of RAM

History
The Spring Project was founded by Stefan Johansson with the goal to replace the TA engine. After some years in development, they have decided to release the game under the GPL. The decision to open source the project is a very difficult choice for Stefan Johansson and his team because they have spent a lot of time developing the engine.

Releases

 * See Spring release history for more information.

Games
These libre games use the Spring engine:
 * Kernel Panic
 * Evolution RTS

These non-libre games also do:
 * Zero-K (CC-BY-NC music)
 * Spring: 1944 (CC-BY-NC assets)
 * The Cursed (CC BY-NC-SA 3.0 art)
 * Beyond All Reason (CC-BY-NC-ND 4.0 all animations)

Both lists are far from complete.