A few years ago The Register described it as a rack-sized blade chassis with hardware, firmware, and software designed in-house together.

It’s a 7-foot tall rack with compute sleds, storage sleds, and network sleds. It has its own BMC design, its own power design, its own physical connectivity design, its own virtual networking design, its own hypervisor (although it’s based on Bhyve), its own OS (although it’s based on Illumos), and its own API to spin things up and configure them.

As I think of it, it’s basically a private cloud in a box and The Register wasn’t far off.