openbsd-ports/net/pdnsd/pkg/DESCR

pdnsd is a proxy dns server with permanent caching (the cache
contents are written to hard disk on exit) that is designed to cope
with unreachable or down dns servers (for example in dial-in
networking).

pdnsd is configurable via a file and supports run-time configuration
using the program pdnsd-ctl that comes with pdnsd.

Wonder why you should use it instead of BIND?

* permanent disk cache (useful for frequent power-offs/reboots)
* usually smaller memory footprint (depends on cache size)
* offline-detection prevents hangs (e.g. the typical hang on startup
  of some Netscape Navigator versions if not dialed in)
* better control about timeouts (also to prevent hangs)
* better control over the cache
* better run-time control
* strict RFC 2181 matching
* negative caching