This site is the default recommended site to use. It's been fully tested and will not have any downtime.
Beta Testers Site
This site is a half way house between the development and production sites. It's functionality should be stable however users of this site may encounter bugs and are encouraged to report these to the developers. This site will most likely contain features and content which will soon be available in the production site.
This site is best avoided by everyone except developers. Functionality upon this site can be unstable and can change without notice. Any changes that are made by developers will instantly be visible upon this site.