The Fretboard is a pretty simple Arduino project that visualizes the build status of up to 24 projects with an addressable LED array. The latest incarnation of the project is housed in an old classical guitar that has be sacrilegiously chopped in half. Fret board .. threat board .. you get the idea?
The embedded Arduino uses an ethernet shield to poll for build status and update the LED display. Given the minimal processing capabilities in an Arduino, it gets the build status in simplified form from an HTTP 1-compatible proxy.
All the hardware design and software is open-sourced, including the proxy server.
I've been running this at my workplace for a couple of years now. Originally I had 22 projects running on Cruisecontrol, but now I've switched it over to a full complement of 24 projects building on Circle CI. Other CI build systems are trivial to add.