One of the things I think we'll need to address within our Arena ChMS Community is the ability to have (manage) multiple developer custom projects. While its possible to do this without a tool, its terribly inefficient and not recommended.
SharpForge is an open source .NET 2.0 (C#) software project hosting web application that promises to be an easy way for teams within your organization (ie, the Arena Community) to manage and share their projects. (Think SourceForge or CodePlex but you get to install it on your own server for your own private/public organization.)
Features include release repository, source code repository w/Subversion support, forums, work item tracking, wiki, and chat.
I think the system looks promising and has potential, but as it is currently in beta, there are some problems (just viewing the site in IE 6 caused my IE to crash three times). Go check out their site http://sharpforge.org/ but go there with Firefox or trying IE7.