Mdnsd

mdnsd, a simple embeddable Multicast DNS Daemon, was originally released by Jeremie Miller in 2003.

It has not been updated since. There is a github project trying to revive it at https://github.com/troglobit/mdnsd

Modern alternatives

The avahi-daemon is a mature Multicast DNS implementation which also does Zeroconf. It's highly configurable. That's probably what you are looking for (avahi-daemon manual).

systemd-resolved, which is part of systemd and likely already installed on your system if you are using a modern Linux distribution, has a simpler Multicast DNS feature. See the systemd-resolved manual for details. tl;dr is to set MulticastDNS=yes in /etc/systemd/resolved.conf