Graphicall.org

When you really start getting into Blender, it can become highly addictive. One of the huge benefits of Blender being open source is the sheer amount of access you have to developers and, by extension, development versions of Blender.

Graphicall.org is a Web site set up by Blenderheads to provide everyone with periodic builds from the development source tree. Builds are created for each of the major platforms Blender supports, and they're uploaded to the site with incredibly high frequency. There are automated daily builds, and some users even upload builds more than once in a single day. This way, regular users can play with new features while they're being developed and, hopefully, contribute to the process by creating bug reports and providing feedback to developers. This level of access is unheard of for regular users of any of the proprietary 3D packages, and it's one of those things that you get with Blender precisely because it's open source.