Shared by Raspberry Pi Magic Mirror
The Cluster HAT interfaces a (Controller) Raspberry Pi with 4 Raspberry Pi Zeros (NOT included). Configured to use USB Gadget mode, it is an ideal tool for teaching, testing or simulating small scale clusters.
The folks at Adafruit are busy as a bee working on bringing some of their really cool boards to the Raspberry Pi platform. Here's a few that came in over the last few days: 16 servos is almost to.