Knot DNS is a high-performance authoritative-only DNS server which
supports all key features of the domain name system including zone
AXFR and IXFR, DDNS and DNSSEC.  Its key features:

 * Open source
 * High-performance, multi-threaded, and mostly lock-free
   implementation which scales well on SMPs
 * Object-oriented design
 * Support for all important DNS protocols:
   - Full and incremental zone transfers
   - EDNS0 and DNSSEC extensions, including NSEC3
   - NSID

WWW: http://www.knot-dns.cz/