Author: Erwin Hoffmann. IPv6 capabilities have been included by Felix von Leitner's IPv6 patch. The original ucspi-tcp 0.88 is by D.J. Bernstein
ucspi-tcp6 is a fork of Bernsteins' ucspi-tcp 0.88 program, which includes, among the other things, ipv6 capabilities to the original ucspi-tcp. tcpserver and tcpclient are easy-to-use command-line tools for building TCP client-server applications.