Cassini; We’ve all used it and loved it, now it’s the end of the road for the visual studio webserver.

It gets replaced by  IIS 7.5 Express

• You can install it on its own. It's IIS, except it runs as a user process rather than a service. Cassini (Visual Developer Web Server) is dead! It's "just in time" IIS. There when you need it, and not running when it's not used.
• This is the web server that Web Matrix uses today, but it'll be enabled in Visual Studio 2010 when SP1 comes out.