Grove
12/22 I got some Grove parts including Can Bus adapters from Seeed Studio, some proto boards, and a Pi hat.
Grove CAN BUS Module
"based on GD32E103" https://www.seeedstudio.com/Grove-CAN-BUS-Module-based-on-GD32E103-p-5456.html It's made by Longan Laboratories
It has a 120ohm terminating resistor on the board, you have to solder a jumper to enable it.
I think it's got a TTL level UART on it so it would go to the RPISER port on the GrovePi0 Pi Hat
Pi Hat
The one I have is this one: https://www.seeedstudio.com/GrovePi-Zero-GrovePi0.html but I find it unlikely I paid $25, I probably got it on a clearance deal.
Made by Dexter Industries GrovePi0 https://www.dexterindustries.com/GrovePi/engineering/port-description/ It has an Atmel Mega328P on it so it's actually an Arduino in disguise. It has 6 Grove ports. They all pass through the Mega328P and are connected to the Pi I2C. https://www.dexterindustries.com/GrovePi/engineering/software-architecture/
A0
A1
A2
RPISER
D3
I2C
A different product entirely: https://wiki.seeedstudio.com/Grove_Base_Hat_for_Raspberry_Pi_Zero/ This $9.80 board has its own ARM Cortex M0 MCU.
Both of these boards seem like they happily work without being attached to a Pi.
The board includes a 12-bit ADC with 3 analog Grove ports. The UART port passes through to the Raspberry Pi GPIO on GPIO14 and GPIO15. There is a port that lets you burn new firmware into the Cortex MCU.