Mdns-scan is a tool for scanning for mDNS/DNS-SD services published on the local network.

It works by issuing a mDNS PTR query to the special RR _services._dns-sd._udp.local for retrieving a list of all currently registered services on the local link.

mDNS/DNS-SD is part of Apple's Zeroconf strategy (a.k.a. Bonjour). The avahi-daemon package is an implementation of mDNS/DNS-SD.