I would like to assemble a list here of Pi Zero format Expansion Hats.
Lets start with a board that I know is supported on FreeBSD and we will go from here:
makerspot.com
In the same vein I just ordered something with terminal blocks:
alchemy-power.com
I have several more Pi Zero Hats on the way.
What are you using?
Lets start with a board that I know is supported on FreeBSD and we will go from here:

Prototyping Board for Raspberry Pi Zero
DIY electronics and kits half size breadboard, compatible for Raspberry Pi Zero project.

In the same vein I just ordered something with terminal blocks:

PiZ-EzConnect - Connect Pi Zero to the Real World - Alchemy Power Inc.®
PiZ-EzConnect allows easy connection of sensors and other electronics devices/components to GPIOs on a Raspberry Pi via solder points or terminal blocks

I have several more Pi Zero Hats on the way.
What are you using?