The PowerDNS server 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. Additionally, through use of clever programming and caching techniques, PowerDNS offers very high domain resolution performance.
Prime examples of backends include relational databases, but also (geographical) loadbalancing and failover algorithms.
The PowerDNS recursor daemon which is also part of the PowerDNS compilation is a dedicated high performance recursive (aka caching-only) Nameserver that already powers some larger broadband ISPs and as of late learned to embed Lua Scripts making it possible to manipulate DNS Answers from within those Scripts. [Less]
Eventlet is a networking library written in Python. It achieves high scalability by using non-blocking io while at the same time retaining high programmer usability by using coroutines to make the non-blocking io operations appear blocking at the source code level.
A utility for running arbitrary commands when files change. Uses kqueue(2) or inotify(7) to avoid polling. `entr` was written to make rapid feedback and automated testing natural and completely ordinary.