(A bit off-topic)

Locally hosted web apps are on the rise (Mailpile, Camlistore, etc.) and remembering which app runs on which port is neither user-friendly nor scalable. More so if you start to consider multiple users on the same machine.

Maybe there's a need for a usable reverse proxy just for local web apps?

It would also be neat if browsers could speak HTTP over some IPC that isn't TCP on some random port. Maybe UNIX sockets in ~/.run? This would delegate read/write permissions to the OS.