Posadis is a domain name server for Unix and Win32 systems. It can both act as an authoritive and as a caching DNS server, and it supports standard DNS master files, zone transfers, and DNS Notify. Its modular structure allows plug-ins to define new zone types and add new functionality.
Poslib is a library which provides easy access to the Domain Name System. The client part can be used to create DNS client applications, while the server part lets you easily create a multi-threaded DNS server program, portable to many operating systems including Linux, FreeBSD, and Windows.