Links to..?

what on earth are you talking about
like when you're using anchor tags?
or like..*shrug*

Well, i guess, as many as there are programs that support it. As long as you can tell the browser (or the system etc) what to do with various protocols, just about anything is possible. Standard ones include the one you listed above, ftp://ftp.host.com will launch an external FTP program (or browse in FTP mode on some browsers, or mount the server as a volume in OS X)...

I don't really know that there's a list, since it's up to 3rd party developers, there aren't strict standards, besides the main ones.

paul