This tip depends on knowing how to use Alert boxes from the command line – – read that tip first.
If you and a friend are both running BeOS, you can use alert boxes to communicate with one another. For example, telnet into your friend’s machine and type:

 alert "Loan me five bucks?" Yes No 

A dialog will pop up on his screen. If he clicks Yes, „Yes“ will be spit back out to your command line, and vice versa.
Here’s a screenshot on using Alert boxes, taken from the BeOS Bible.