NSD is an authoritative only, high performance, simple and open source name server.
Unbound is a validating, recursive, and caching DNS resolver.
BIND is open source software that implements the Domain Name System (DNS) protocols for the Internet. It is a reference implementation of those protocols, but it is also production-grade software, suitable for use in high-volume and high-reliability applications. BIND is available for free download under the terms of the ISC License, a BSD style license.