Another use I had for a Small Board Computer was as a door security system. The Raspberry Pi with attached Adafruit touchscreen and camera would be perfect for this. Also add a magnetic sensor for “door open”, and a more general motion or even position sensor.
I actually got most of the way through the basics of this project. One of the problems I ran into was getting a clean picture to the rpi’s camera through the door’s existing peephole. It would probably be best to figure out a solution better suited to the camera, and just swap out eye-pieces when the door camera is installed (remembering to keep the original one for replacement if you ever need to).
The basic idea is to have the camera simply display what it sees to the screen, with a push button to turn the screen on/off. Part of the screen display could be overlayed with things like door status (open/closed), positional and other sensor information. The screen should be movable, or mounted in a direction that people of all heights can see who is knocking at the door.
Ideally it would be nice to also have this video also be streamed to an installed security monitoring system, like “motion” or other open source camera stuff. I’m also not sure how feasible audio recording would be.