NuPack is an open source open source package manager for .NET. No that isn't a mistake - it is open source and it manages open source packages.
It enables open source projects to integrate there code with Visual Studio and hence gain greater use. Once installed in Visual Studio NuPack lets you browser for possibly useful packages and then install and use them within a project. It isn't just a download manager as it also handles dependencies, modifies configuration files and can perform intelligent updates and removals.
Documentation and tutorials on nupack.codeplex.com
You can download the beta using the Microsoft Web Plaform Installer.
The final announcement concerned WebMatrix beta 2. WebMatrix is a lightweight development tool using IIS Express, SQL Compact Edition and some ASP .NET extensions. It provides yet another way you can build a web site using Razor syntax. The latest version features Razor in both VB and C#, more templates and NuPack integration. A new toolkit provides helpers for easy inter-working with Facebook, Analytics, Twitter, etc.
You can find more out about all three at ScottGu's Blog.
Microsoft WebMatrix and Razor
MVC - it's the routing stupid!
ASP.Net MVC in Action