Unbound is an open-source DNSSEC validating DNS resolver.
Unbound is an open-source BSD licensed caching DNS resolver developed by NLnet Labs, and is included in FreeBSD & OpenBSD's base installation.
In addition to dnssec validation, Unbound implements many enabled-by-default security features including hardening, cache poisoning prevention and zone overrides. Guides are available in the Documentation for configuration, and the underlying libunbound C library.
Documentation: https://www.unbound.net/documentation/index.html
Unbound(8) https://www.unbound.net/documentation/unbound.html
Unbound.conf(5) https://www.unbound.net/documentation/unbound.conf.html