NSD

NSD, the NLnet Labs Name Server Daemon, is an authoritative, RFC compliant open source name server built for reliability and correctness above all else.

Its credibility comes from where it is deployed. NSD runs on several of the DNS root servers, and the root server operators deliberately run different implementations so that a single bug cannot take down the whole system. Being one of the implementations chosen for that role is a meaningful endorsement of both the code and the project behind it.

The design is authoritative only, which keeps the codebase small and the attack surface narrow. NSD is often paired with Unbound from the same organisation, splitting authoritative service and recursive resolution into two separate programs rather than combining them, so a compromise or failure in one does not affect the other. That separation is a security position, not just an architectural preference.

NLnet Labs is a not for profit foundation, which shapes the project differently from vendor backed software: there is no commercial pressure to add features that complicate the core, and the organisation's stated purpose is the health of the open internet infrastructure itself. The software is distributed under a BSD licence, supports DNSSEC, and is available packaged by most Linux and BSD distributions as well as from source.