Non ci posso credere... 
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.
Source:
PHP on .NET