For a musician, nearly anything can be used as an instrument: Garbage bins can be played like drums; rubber bands can be plucked like the strings of a bass guitar. Even your own hands can be employed as an instrument (for reference, it's the harmonica).
Nonetheless, I've never seen an “instrument” quite like this before.
Created by Swedish musician Martin Molin, the Wintergatan Marble Machine is a massive, wooden contraption that uses marbles (2,000 of them, to be exact) and a hand crank to “play” various instruments simultaneously.
Hidden in the body of the machine are a series of instruments, including a kick drum and bass guitar. When the crank is, uh, cranked, the marbles are released onto a conveyor belt which randomly drops them down chutes, each leading to a different instrument.
The resulting sound has a poppy, almost electronic-y vibe reminiscent of pretty much everything on the Top 40 charts.
See the incredible instrument in action below.