Over the course of this year, I've acquired six Raspberry Pi model 2 B computers, and configured them in a cluster (or 'bramble') so I can use them to test different infrastructure configurations, mostly for running Drupal 8. All the Ansible playbooks and instructions for building the cluster are available on the GitHub project page for the Raspberry Pi Dramble.
Each Raspberry Pi has its own RGB LED board that's wired into the GPIO pins, so they're controlled by software. I can demonstrate different ways of managing the cluster via Ansible, and I finally took the time to make a video, Ansible 101 - on a cluster of Raspberry Pi 2s, which shows how it all works together:
The video demonstrates Ansible's simple and powerful model of SSH-based infrastructure management visually. It's been a lot of fun building the Dramble and hacking both the hardware and the software to make this presentation possible!
Since building the Dramble, I've taken it with me to presentations at MidCamp in Chicago, DrupalCon in LA, and local meetups in St. Louis (like the first ever Ansible St. Louis meetup!). I've also used the cluster to debug some hard-to-reproduce infrastructure and performance problems in Drupal, and I hope to continue finding fun new things to do with it!