For those who have never heard of it Cassini is a tiny little web server written in .NET, for those who have, its really neat and handy.

I had a chap who wanted to demo some static HTML mockups to clients, but for some reason (XPSP2) I.E. was bitching about activeX controls because he was running off the local file system.

One Simple install of Cassini, register the cassini DLL in the GAC (Very important gives bogus conflict error otherwise), and he was away a simple quick solution and portable solution to that problem without the need to resort to a full blown IIS installation.