This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Run netstat command on the command line. It will tell you which application is listening on which ports. I think the parameters to netstat change based on OS, although I might be wrong there. Look at the help for netstat