All I have to say about this bike hack is you better really know your local public-transit schedule, otherwise you might wind up smashed against the windshield of an angry conductor's streetcar, traveling backward and flailing like an injured bird.
The bahnradbahnrad, which Google translates to (far as I can tell) "track bike track bike," turns the negative of accidentally slipping your bike wheel into a streetcar track and falling down into the positive of a potential straight-line commute across town. It was built by the German urban collective We Are Visual, who used it to ride the rails in Kessel like they were pumping an old-timey handcar.
There might be a slight stigma to the hacked bike if you think training wheels are uncool. How does it handle cornering, and will the wheels last for long against the constant friction of the metal grooves? Still, for an effortless ride around all the city's major destinations, this idea gets a gold sticky star.
As a commenter on Vimeo noted, something like this has been done before with children, as well as one old man who thinks he's a locomotive:
(H/t to urbanshit.)