This will allow you to send morse code through radio waves to another computer. This could be used as a sort of chat program.
Step 1: Gather Supplies
You will need very few supplies:
-A crystal oscillator (will talk about which kind in the next step)
-A 9 pin serial jack (D-SUB9)
-A little bit of wire
-Something to use as an antenna
-A male to male audio jack (unless you know morse code)