"Found this on my front porch today. Two battery packs, some sort of circuit board assembly, and a microcontroller thing. What is this thing?"
A: "We’re looking at multiple parts here. The board at the right of the photo is an Adafruit Feather STM32F405 microcontroller, as you surmise. The board at the left of the photo doesn’t seem have any model number on this side, but it appears to be a radio board — that’s a coax connector for an antenna at the lower left. It also shows the Adafruit logo, so it’s prolly sold as an I/O board for the controller. The foam is likely just scrap being used as a cheap non-conductive mounting surface."
For you younger guys. Dating was much more fun before pantyhose.
It is used to keep the pistons from the disk brake caliper separated when the wheel is removed in case the brake lever is pushed accidentally.
It's from Adafruit, the company famous for their DD8008S and attempted takeover of Apple... so everything else is obvious.