In what's probably the coolest custom-built machine I've seen in ages, computer enthusiast Michael J. Mahon has built a parallel computer made out of 17 Apple IIe motherboards.
As you can see the "AppleCrate II" looks like a big crate of motherboards stacked on top of each other -- and that's pretty much what it is, along with some very clever networking and custom boot code.
This is actually his second computer built using old Apple motherboards. The first we covered