TCP2Serial is a utility application to proxy traffic to/from a serial port over the network. For example, you run TCP2Serial on your mac with a serial port attached and connected to a serial device.
An example use case: You could use this app on a laptop that has a serial adapter connected to a router/switch that is down. Your network engineering team could them telnet to the computer hosting TCP2Serial to configure the router/switch.
NOTE: More than one telnet client can connect. Text received on the serial port is echoed to all connected telnet clients.
One further note, this app can't do anything without a serial port. Since most Mac's now-a-days don't have built-in serial ports you'll need a USB serial port.