Network discovery on a Mac

There is a program called Bonjour Browser that will list well known services that have registered on your local network. I believe that most Macs have one or more registered protocols by default.

ping the broadcast address (the broadcast address is printed as part of the output to ifconfig en0)

The hosts answering are on your local network. (You may also try arp -a but that only keeps track of recently contacted hosts so you may want to run it after the broadcast.)