BRS WebWeaver is a standalone http/ftp server for the win32 platform. It supports cgi, isapi and php along with aliases, authentication and everything a good web server needs.
It is not as tightly integrated into Windows as Microsoft's Personal Web Server and, unlike PWS, very lightweight which makes it the ideal test platform for your own sites or allows you to quickly share the occasional file without tweaking with Windows' security.
Please take notice that these guys worked hard for a free product. Consider making a small donation when you find their software useful.