CVS

Quote from WikiPedia:Cvs :

"The Concurrent Versions System (CVS), also known as the Concurrent Versioning System, implements a version control system: it keeps track of all work and all changes in a set of files, typically the implementation of a software project, and allows several (potentially widely separated) developers to collaborate."

CVS is also what the Vegastrike developers use and if you would like to contribute you can find a guide for checking out CVS here: HowTo:Checkout CVS