Simplest screen echo server?

Question

What is the simplest way to do the following thing?

Run a program which will open specified port, listen for it, and display whatever it receives. Also if type something -- then send back to connected peer.

This is for debug purposes.

Answer 1

Server listens on port 8000:

$ nc -l 8000

Client connects to port 8000:

$ nc localhost 8000 

Answer 2

This sounds like a job for Gnu Netcat (nc)