The small board on the left is unmistakably a Teensy 3.2:

https://www.pjrc.com/store/teensy32.html

As to what it's doing in there, I have no idea.

Well, I'll be darned! I wonder if Paul Stoffregen knows about that!

edit: probably? It was posted at the Teensy forum about a month ago.

https://forum.pjrc.com/index.php?threads/the-deepest-teensy....