

I’m probably doing exactly what they want here (e.g. having a conversation about it), but that letter is called “Eth” and was the Old English way of spelling the “th” sound: https://en.wikipedia.org/wiki/Eth
A number of linguistic buffs want to bring it back to the modern English alphabet.
Back when I was in high school, we had a shared pool of laptops stored in the library, and our teachers would reserve the library space for days when we were supposed to be working on laptops. My district had a bunch of Dells with the nipple mouse. To this day I still think it’s probably the most convenient and precise input device I’ve ever used.