How can I allow two applications access to the same serial port

Question

I need two application to run on the same serial port (/dev/ttyUSB0). One is a read-only monitor, while the other is an application that will read the data on the serial port and respond back.

How can I make it so that I can have two applications run on the same serial port, if the monitor can only read incoming messages, then that is fine.

I heard that socat can do something like that, but can only find information about it making virtual ports and not using physical ports, what I want is for get to take a physical serial port, and make a copy (or two if necessary) of the serial port for the monitor to be able to read incoming messages.

I am using a Debian OS