Here's a thing i built nearly 3 years ago -- a Raspberry pi sandwich. It's four RAspberry pis (Original models) in a sandwich, for extra delicious.

Today they run Openhab, mysql, a Salt master, and they talk to each other with Consul (and some dnsmasq). They now have other raspberry friends in the house (more raspberry pis, doing more things) and even some Beaglebone cousins to talk to.