When I was younger I worked at a retail store and I remember being thrilled to discover I could telnet into a cash register and echo text directly to the attached receipt printer.[0] I became a small time hero at one point when I used this power to alert our sister store that their phones weren't accepting calls during the middle of the holiday season.

[0] Also interesting is the time I discovered that sending a special escape code to the printer caused the cash drawer to open, but that's a tale for another thread.