P.U.R.E. was built using the Spring Engine. This is a great Open Source engine for RTS games.
Visit the Spring Engine website at www.springrts.com to learn more about this great engine.
P.U.R.E.'s source is included in every build, and is free to use for whatever you wish.
We also make available World Builder, our level-development tools and a large amount of free, Open Source content we've built.