Microsoft has released CodePlex Beta which is kind of like Sourceforge on top of Team Foundation Server.  You can create a project to be hosted on CodePlex, or download the software and run it on your own machine. 

Some of the projects hosted on CodePlex right now include:

• “Atlas” Control Toolkit
• CodePlex
• Commerce Starter Kit
• Connected Government Framework
• IronPython
• MSBuild Extras – Toolkit for .NET 1.1 “MSBee”
• Team Foundation Server Administration Tool
• Turtle – Open source client for Visual Studio Team System

The description on the project website is:

CodePlex is an online software development environment for open and shared source developers to create, host and manage projects throughout the project lifecycle. It has been written from the ground up in C# using .NET 2.0 technology with Team Foundation Server on the back end. CodePlex is open to the public free of charge.

CodePlex includes the following features:

• Release Management
• Work Item Tracking
• Source Code Dissemination
• Wiki-based Project Team Communications
• Project Forums
• News Feed Aggregation