I've done digital signage, controlled servos, used them as cameras, the works.

Right now I have:

- A 5-node Pi 2 cluster running k3s.io (https://github.com/rcarmo/raspi-cluster), and a separate Pi 2 I use as a Docker build box and local Docker registry.

- A Pi 3B+ as a "lab" desktop computer with an USB oscilloscope and FTDI cables to flash ESP8266 and Arduinos

- A Lakka.tv arcade/MAME box for the kids with a PS3 controller (no room for a proper PiCade, we just use the TV(

- A Pi 3A+ with a mic array for playing around with Google Assistant

- A Pi Zero W taped to the inside of my electricity meter trying to estimate power consumption (we have a spinning disk mechanical meter)

- Another Pi Zero W that I use to demo Azure IoT solutions

- An ODROID U2 (Could be a Pi) running HomeKit and Node-Red for home automation, as well as a bastion container (all dockerized).

Edit: forgot about the 3B hooked up to my 3D printer running OctoPi

And the list goes on. I have many older Series Bs lying around, and once used one to revive a dead synth whose MIDI keyboard still worked (I set up timidity and a sound font on it and it became the kids' piano). I also ran a Plex server on one until it became obvious that I needed to think about transcoding (but it worked fine for music).

You can do a _lot_ with Raspberry Pis, and I fully expect to get a beefy Pi 4 to use as a lab computer.

I just hope they also beef up the Zero at some point (power envelope will be a problem, but a Zero with Pi 2 specs would be great).