Ucspi-tcp

ucspi-tcp is a public domain Unix TCP command-line tool for building TCP client-server applications. It consists of super-server "tcpserver" and "tcpclient" application.
From "Life with qmail", Dave Sill, 2 January 2006 (Appendix B.3.): "ucspi-tcp" is an acronym for UNIX Client-Server Program Interface for TCP, and it is pronounced "ooks-pie tee see pee".
tcpserver features built-in TCP Wrapper-like access control.