libunp is the library used in W. Richard Stevens' book "UNIX Network
Programming Volume 1, 2nd Edition".  It contains the library and headers
used in the examples as well as all programs from the text that compile on
FreeBSD systems.

For more information on the book, see

http://www.phptr.com/ptrbooks/ptr_013490012X.html

For more info on W. Richard Stevens, see