Some days you don't want to save the Princess yourself, you just want to watch someone - or something - else do it.
A modder, calling himself "pjgat09," has built an NES controller that can play games by itself, using information harvested from the speed run community to tell it what to do. Using this data, the controller is capable of completing Super Mario Bros. in around five minutes.
The information is loaded onto a flash card and run through a microcontroller that can interpret it, and convert it into button presses that the NES console can understand. The code in this particular video comes from the fastest known tool-assisted speed run of Super Mario Bros., which uses emulation - not to mention a few glitches - to clock the best possible time. Pjgat says that emulators are usually too different from the actual consoles for this to work, but in the case of NES games, the two are close enough that the emulator code can be adapted.
Pjgat also provides detailed instructions on how to build your own robot controller, including how to wire it all up and how to get the speed run data - known in the TAS community as a "movie" - working with the microcontroller. It seems like a pretty painstaking process, but it could be a fun project as long as you don't mind sacrificing a NES pad to get it to work. Pjgat encourages people to experiment with different movies, although he warns that not all of them will work