Release system popularized by the Mozilla browser releases. Instead of releasing Alpha and Beta releases, the programmers set goals in the form of milestones as to when they would release the code. You could always access CVS snapshots, but most people just previewed the releases at the milestone releases. I believe there was originally 15 milestones planned for Mozilla, although that number may have changed. It is also rumored that several Mozilla-related projects such as DOSzilla and Jazilla are using this system. It's a good idea.