mDNS Responder with Unicast runs on a server anywhere in a network and responds to mDNS queries across the network by performing a unicast DNS lookup and returning the result. Many networks use a .local top-level domain for their intranet. This has proven to be quite problematic as operating systems such as OS X have begun handling .local domains differently (in particular, prioritizing multicast DNS over conventional unicast DNS). Ideally, you'd have no problems moving away from a .local domain name, or simply not using one in the first place. That's not always possible, though. So with this tool, a lookup for "host.local" will be resolved via your existing unicast DNS servers, even if "host" does not have its own mDNS responder. Of course, the tool isn't limited to just .local domains, and can realistically work on any network where mDNS is in use.
radns is a small, portable client-side implementation of the RDNSS option in IPv6 Router Advertisements (RFC 5006) that is used to get the address of a resolving DNS server. It listens for Router Advertisements with the Recursive DNS Server (RDNSS) option and stores the addresses in a file following the same syntax as resolv.conf. It optionally calls a script to handle, for instance, DHCP clients that compete for ownership of /etc/resolv.conf or to set the DNS server on systems that don't use resolv.conf at all. It can be easily integrated with the resolvconf(8) program.