I know little about web servers, IIS or FastCGI, but this sounds like it
may enable better support and/or performance of Rails on IIS.
“Microsoft plans to develop and release an Internet Information Services
(IIS) add-on component, FastCGI, that will serve as the interface
between PHP and the IIS Web server. Microsoft expects that this FastCGI
component will be made freely available from Microsoft on
http://www.iis.net for users of MicrosoftÂ® WindowsÂ® XP, Windows Server
2003, Windows Vistaâ„¢ and Windows Server â€œLonghorn.â€”