The Celtic Christmas kit is 4 PCBs built on a single board which break appart and are soldered into a 3D celtic knot shapped like a christmas tree.
Each of the 4 PCBs contain the same circut. Actually, it is the same circut and program as the heart, dragonfly and shamrock. Specifically, there are 4 Attinys wich each controll 20 LEDs which blink independantly. The LEDs are controlled by charlieplexing.
For more information on charlieplexing watch this video:
How it was Designed: