Rob Paisley has a page of model railroad circuitry, including, most interestingly to me, a driver for stepper motors. You’d use stuff like this if you wanted to have people moving around inside your buildings, or if you wanted other moving parts on your layout.
I used to build electronic circuits, when I was a sophomore and junior in high school. It’s been so long now that I don’t even remember what all of the symbols mean. It’s almost sad.

But the good news for me is that I’ll be able to build all kinds of cool stuff once I figure it out. I’ve got lots of old 5.25-inch floppy drives in my basement, with stepper motors ripe for harvesting. A stash of 5.25-inch floppy drives with amber LEDs would be a railroad scratchbuilder’s dream, wouldn’t it?