NSD is an authoritative DNS name server designed for environments where speed and stability matter most. It only answers queries for the zones it serves and deliberately performs no recursive resolution or caching; for that, its developer points to the Unbound resolver. NSD includes a fast zone-file parser and, according to its developer, is used by root name servers and many top-level-domain registries. It is self-managed software that you install on your own servers; paid support with a service-level agreement is available.
NSD is developed by NLnet Labs, a Dutch non-profit foundation (public benefit organisation) with an office in Amsterdam. The software is open source under the BSD licence, so it can be inspected and used freely. Because you run NSD yourself, you decide where your zone data and DNS traffic are processed, and there is no commercial owner outside the EU. For a European organisation that wants to serve its own domains authoritatively without depending on a hosted service, it is a suitable building block.