EDIT: Um, better title would be Portless Transport.
I find it tricky these days to come up with a unique IP port number to use with various server applications that I write. There's no guarantee that what you choose won't conflict with someone else's software.
To this end, what I've been thinking about is a special service running on a single port, that you can query (via XML, seeing as the kids think it's cool) to find out what named/GUID services are available and then pass traffic for that service through that same port (like an aggregate).
Is there anything like this already available?