One is an interface for a MIDI controller I use to be able to control the Soundcraft UI16 mixer I use for my desk setup. I'm a bit of an audio nerd, having done pro-am music production, and having a love for broadcasting, and what started as a simple setup to get good quality sound at low latency has now become an audio chain with a teleconferencing audio processor, a headless digital mixer, and several microphones to do acoustic echo cancellation and noise cancellation so I can use an open microphone without headphones.
My mixer, being headless, has no physical controls. From my DJ days, I had a MIDIFighter 3D controller not being used, and a Raspberry Pi without a dedicated task. I was able to write a small bash script to read note information from the controller and send web requests to a Bitfocus Companion server to act as API intermediary between my mixer and the controller. Now, I have physical controls for hardware muting my microphone, and the various computers at my desk. It's effectively a big Elgato Streamdeck for what I use it for, but to be able to upcycle the hardware has been quite nice.
I also was working from home with some long hours, and I wanted to try and improve my sleep schedule. I already use redshifting software (usually what's built into the OS these days, although I used to be a longtime F.lux user), and that's been great, but I also wanted to control monitor brightness by time of day. Giving my eyeballs less light blasted into them has helped me regulate my sleep better. I wrote a small python daemon that can run on Mac or Linux, integrate with native DCC tooling to send control commands to my displays, and gradually adjust the brightness of my monitors based on the time of day. This has also been eternally useful when, being an ops guy, I'm called in during the middle of the night, sit down at my desk to address an outage, and my eyeballs are bombarded with significantly less light, making the pain of adjusting much less difficult to address, and also making falling back asleep after the incident is resolved much easier.