I did a lot of coding for these in the UK during early 2000s.

They were pretty nifty for their time, but I guess completely superseded by RFID.

Always annoyed me that it clearly has 2 wires (power/signal + ground).

They’re used for proofs sometimes, if you expect your security company to do a specific route they need to go to each token on it and touch them, you see iButtons glued to walls outside commercial buildings for that purpose. Systems like that mean they can’t just say they walked the route and go home, I’ve seen them at airport bathrooms for the same reason.

If you are much into Arduino type things you will come across 1-wire as one of the most popular temperature sensors is a DS18B20.

The only place I've run across it in the wild is inside an SGI Octane. I thought it was a battery to replace, but it was actually a "Number in a Can" iButton. It's a read only memory that contains the MAC address and some other stuff. Software gets licensed to this ROM, so if your system breaks you can take the iButton out and move it to the replacement.

It was rather widely used around here in Europe as a "key" to enter building hallways. They've been mostly replaced with NFC fobs nowadays (most of them using very vulnerable chips though).

My dad had an immobilizer built into his car (a 1994 BMW 320 bought in Europe) which used this kind of key. I've almost forgotten about this detail until I stumbled upon this post. I don't know if it was stock, though.

I remember this being in the transit system in Istanbul.