Unbound!

BIND is by far the most widely used DNS software on the Internet. On Unix-like operating systems it is the de facto standard. It provides a robust and stable platform on top of which organizations can build distributed computing systems with the knowledge that those systems are fully compliant with published DNS standards.

PowerDNS is a DNS Server that runs on most Unix derivatives. PowerDNS features a large number of different backends ranging from simple BIND style zonefiles to relational databases and load balancing/failover algorithms. A DNS recursor is also included as a separate program.

The djbdns software package is a collection of Domain Name System tools created by Daniel J. Bernstein. It includes software for all the fundamental DNS operations and several DNS debugging tools which administrators use to diagnose misconfigured remote servers. As of 2004, djbdns's tinydns component was the second most popular DNS server.