The Spark/Ada-based Ironsides DNS server just arrived to FreeBSD ports. I believe it is currently unavailable on all other platforms. Ironsides has the potential to be a showcase for Ada so I'm glad to give it exposure and chance to be used on a great server platform. From it's website:

IRONSIDES is an authoritative DNS server that is provably invulnerable to many of the problems that plague other servers. It achieves this property through the use of formal methods in its design, in particular the language Ada and the SPARK formal methods tool set. Code validated in this way is provably exception-free, contains no data flow errors, and terminates only in the ways that its programmers explicitly say that it can. These are very desirable properties from a computer security perspective.

IRONSIDES is not a complete implementation of DNS. In particular, it does not support zone transfers or recursive queries. It does, however, support a sufficient number of DNS records to be useful as an authoritative DNS server for an enterprise.