Specifically, Joules is a robotic stoker for your tandem bike, when you are riding solo on a tandem.
This project definitely has a steam punk flair, and combines some art, whimsy, and a good deal of engineering. Joules was built by engineer Carl Morgan with his son, a former pro cycling racer. The web page with more information on Joules is here.
Carl has a great U tube video also, linked below.