I haven't read it too carefully but typically something like this would be done by having one program run on the port in question and then it would determine which protocol a given connection is speaking and hand it off to a different port based on config. So your https and ssh servers run on, say, 2000 and 3000 and the protocol recognizer runs on 443 and hands off connections to either 2000 or 3000. See, for example, reverse-proxying with nginx or haproxy.

For the case of ssh versus ssl the detection is trivial: first message for ssl comes from client but for ssh first message comes from server. So server simply waits for a while and assumes that client speaks ssh when it does not receive anything.

One can also match whatever is received in first message from client against known protocols (this approach makes it possible to for example run HTTP and HTTPS on same port as is done by IPP servers, particularly CUPS).