Filed in the interesting, but probably won't use category...
http://www.php-compiler.net/ - some people have written a PHP implementation built on top of the .NET platform. What's more shocking? Some initial benchmarks have it out-performing PHP on Apache. The developers said they are not Mono compatible yet, but something they'll be looking at.
What I'd be most interested in finding out is did they build on top of the HttpRuntime? I wrote a light-weight Cold Fusion implementation on top of the HttpRuntime a long time ago, so I know something like this would be possible - or did they write all the plumbing themselves. If the core is built on top of the HttpRuntime it would make integration of PHP and ASP.NET applications together on IIS amazingly easy.