Subversion

Subversion is a version control system gets it's roots from CVS. Version control is a big part of software development. Here at work we rely on it exclusively for our ever growing code base. Not only is it a great way to keep track of changes you've made along the way. It also has the ability to rollback changes and even revert to any previous version. Subversion is always great in multiple team member environments, you can easily work on the same files without worrying about overriding others changes.