Written by Dan J. Bernstein, tcpclient and tcpserver are powerful easy-to-use command-line tools for building TCP client-server applications. tcpserver provides TCP access control features, similar to tcp-wrappers/tcpd's hosts.allow but much faster; it can run high-availability services much better than inetd.
Real-time Blocking List support is also included in tcpserver, so you can run qmail-smtpd with it and avoid a lot of SPAM.
tcpclient and tcpserver conform to UCSPI, the UNIX Client-Server Program Interface, using the TCP protocol.
Dan Bernstein (ucspi-tcp's author) only gives permission for his code to be distributed in source form, or binary by approval. This package has been put together to allow people to easily build a binary package for themselves, from source.
If there is a package called ucspi-tcp available, then Dan has approved the binary version of the package for distribution, so you might as well install that and save yourself some effort.