Although BIND is the most popular domain name server software being used today, NSD (“name server daemon”) is another popular alternative open-source server program.
NSD is an authoritative name server (i.e., not implementing the recursive caching function by design) and uses BIND-style zone-files (zone-files used under BIND can usually be used unmodified in NSD, once entered into the NSD configuration).
NSD uses zone information compiled via ‘zonec’ into a binary database file (nsd.db) which allows fast startup of the NSD name-service daemon, and allows syntax-structural errors in Zone-Files to be flagged at compile-time (before being made available to NSD service itself).
The collection of programs/processes that make-up NSD are designed so that the NSD daemon itself runs as a non-privileged user and can be easily be configured to run in a Chroot jail (A chroot environment can be used to create re-root a program to another directory in unix), such that security flaws in the NSD daemon are not so likely to result in system-wide compromise.
Most of the Internet root nameservers use BIND, however a few of them also use NSD. Apart from that several other TLDs use NSD for part of their servers.
I have worked on NSD and BIND, BIND is much more better but is much more prone to security attacks