From 10base-t Interactive:
IP Broadcaster and IP Scanner leverage Apple's Bonjour technology to facilitate communication between computers on an ad-hoc LAN. IP Broadcaster is similar to other menubar IP indicators, and can be used as such in a stand-alone fashion. It provides LAN and WAN information for multiple network interfaces and refreshes itself at a user specified rate.
Where this application distinguishes itself is in its ability to broadcast this data via Bonjour to its sister application, IP Scanner, which in turn collects the data from all the IP Broadcaster-enabled machines and sorts them in a column view in realtime, each IP linked to the current username of the person logged in to that machine.