Tiny Titan "supercomputer" uses blink(1) USB LEDs
/This is so neat! A few years ago, the Oak Ridge National Lab created "Tiny Titan", a demonstration of how supercomptuers work using a cluster of Raspberry Pis. It's a scaled down model of the Titan supercomputer. To visualize what each note of the cluster is doing, blink(1) USB LEDs are plugged into each Raspberry Pi, indicating what its up to.
More details from this Popular Science article and the Tiny Titan homepage. Or create your own (since it's all open source) by visiting the TinyTitan github repo at https://github.com/TinyTitan.
(photos courtesy of reddit user "0110010001100010" in this post)