Top 10 Raspberry Pi add-on boards: 
Did you know you can adorn your Raspberry Pi with HATs? Of course we’re not talking about hats like people put on their heads, but rather HATs: “hardware attached on top”. These are add-on circuit boards and accessories that add functionality to your Raspberry Pi.
read more: Opensource.com ben_nuttall
Supporting Open Source.
Have you tried: Diving with Sharks?