The PowerDNS daemon is a versatile nameserver which supports a large number of backends. These backends can either be plain zonefiles or be more dynamic in nature.
Prime examples of backends include relational databases, but also loadbalancing and failover algorithms.
The company is called PowerDNS BV, the nameserver daemon is called PDNS.
PDNS is an authoritative only nameserver. It will answer questions about domains it knows about, but will not go out on the net to resolve queries about other domains. However, it can use a recursing backend to provide that functionality. Depending on your needs, this backend can either be the PowerDNS recursor or an external one.
When PDNS answers a question, it comes out of the database, and can be trusted as being authoritative. There is no way to pollute the cache or to confuse the daemon.
PDNS has been designed to serve both the needs of small installations by being easy to setup, as well as for serving very large query volumes on large numbers of domains.
Another prime goal is security. By the use of language features, the PDNS source code is very small (in the order of 10.000 lines) which makes auditing easy. In the same way, library features have been used to mitigate the risks of buffer overflows.
Finally, PDNS is able to give a lot of statistics on its operation which is both helpful in determining the scalability of an installation as well as for spotting problems.