I think the site is using fastcgi ?
Not really sure, but it's easy to switch between cgi, fastcgi and apache module. With WebDesign package, it can even be done with a single define.
How would you compare "FCL-Web" to the other web development tools like "radphp" ?
IMHO the same as Lazarus + WebDesign package, I haven't tried RadPHP though.
or others like perl, php, xhtml ?
perl and php: interpreted, slow, difficult to debug, but has a lot of frameworks to choose and a big community.
(x)html: well... this one shouldn't be included since this is like the assembly of a web application. Our application (with any other language) should produce this as the final output.