The Flowbee
You hook it up to your vacuum cleaner, and you cut your hair with it. The official Flowbee website describes it best:
The FLOWBEE Vacuum Haircut System allows you to create the most popular haircut styles. FLOWBEE can cut your hair from 1/2" to 6" long in any 1/4" increments. Simply select the desired spacer depending on the length you want your haircut. Then attach the spacer to your Flowbee. Haircut styles of your choice are easy and clean. Longer than 6" haircut is possible with the addition of more spacers available on the parts page. I had a friend whose mom owned a Flowbee (or similar) haircut system. He looked like his hair was cut by a drunken Edward Scissorhands.