ucspi-tcp 1:0.88-7 (amd64 binary) in ubuntu mantic

 tcpserver waits for incoming connections and, for each connection, runs a
 program of your choice. Your program receives environment variables showing
 the local and remote host names, IP addresses, and port numbers.
 .
 tcpserver offers a concurrency limit to protect you from running out of
 processes and memory. When you are handling 40 (by default) simultaneous
 connections, tcpserver smoothly defers acceptance of new connections.
 .
 tcpserver also provides TCP access control features, similar to
 tcp-wrappers/tcpd's hosts.allow but much faster. Its access control rules
 are compiled into a hashed format with cdb, so it can easily deal with
 thousands of different hosts.
 .
 This package includes a recordio tool that monitors all the input and output
 of a server.
 .
 tcpclient makes a TCP connection and runs a program of your choice. It sets
 up the same environment variables as tcpserver.
 .
 This package includes several sample clients built on top of tcpclient:
 who@, date@, finger@, http@, tcpcat, and mconnect.
 .
 tcpserver and tcpclient conform to UCSPI, the UNIX Client-Server Program
 Interface, using the TCP protocol. UCSPI tools are
 available for several different networks.