From the SourceForge FAQ: "SourceForge is a free hosting service for Open Source developers which offers, among other things, a CVS repository, mailing lists, bug tracking, message forums, task management software, web site hosting, permanent file archival, full backups, and total web-based administration."
All of the resources listed above allow any group to easily establish a development environment through which work can be done quickly, easily and safely.
For example, we at the newbieDoc project use SourceForge because it allows us to take advantage of web space, mailing lists, and other features listed in the section What is SourceForge?. The CVS repository is particularly useful as it allows easy peer review of the files it contains.