djbdns!

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.

Knot DNS is a high-performance authoritative-only DNS server which supports all key features of the domain name system including zone transfers, dynamic updates and DNSSEC.