Some of these I had to see animated to even grasp what it might do. Even then I couldn't figure out what use it might be.
A couple of them describe stuff that used it but most were just technical details. It would be nice if there was a link to something that used it so you could see why it was ever made (or maybe some of these are just for fun).
I couldn't get through them all but will come back because it's fun to watch. More fun than it should be really.
You probably have one of these if you have a printer. It's basically the same mechanism as on the output paper guides, that causes a movement of the guide on one side to match the other side, and for the paper path to therefore remain centred.
Normally you can take the output tray off and turn it over to see the mechanism.
For number 115: by moving the bigger piece side to side you spin the two wheels. Each wheel spins the same amount but in opposite directions. Shafts attached to those wheels can be used to drive components that need to move equally but in different directions.
A couple of them describe stuff that used it but most were just technical details. It would be nice if there was a link to something that used it so you could see why it was ever made (or maybe some of these are just for fun).
I couldn't get through them all but will come back because it's fun to watch. More fun than it should be really.
edit: example of one that has me guessing why it exists: http://507movements.com/mm_115.html