There are a lot of great HATs and other expansion boards for Raspberry Pi out there, what is your favourite, whatever project you might be working on?
… or something completely different? 
Would love to hear what do you like to hack on / build on the most! 
You can also share any stories if you have some fun experience!
@imrehg Something different: I spend some time optimizing SD-Card lifetime and one of the things that could instantaneously lead to an instant SD-Card death was switching of the Raspberry Pi when writing onto the Card. I experienced this once. The bootsector of the card was destroyed - the Pi wasn’t able to boot. The card was just about one or two weeks old.
There is a way how to protect your card from this: Safely switching off the Pi. But in some situations this isn’t possible so something like an UPS for the Pi is needed.
After doing some research on this topic I found a few solution in form of an UPS-Hat for the Pi. One of those products turned out to be the best:
It’s a Raspberry Pi UPS Hat that communicates over SPI with the Pi and features wide range Power Input, Li-Ion Support, Battery Charger with integrated fuel gauge and a safe-way Power On-/Off Button, which when you press it, it initiates a shutdown of the Pi and after this has happened the Pi UPS switches off the Power Supply for the Pi.
In fact this Hat really works like a charm but unfortunately the german manufacturer tried sell this the “classic german way” - closed and with intention to make profit based on the hardware. Their mission failed but the product is still available but you can’t get any informations on the code on the Hat (there’s an ATmega controlling and watching the Power Supply).
But for any commercial product that is using the Raspberry Pi (Compute Module) this UPS is a must to ultimatively safe your SD-Card from death.
By the way - when using eMMC you aren’t safe from getting a corrupt Boot Sector since the eMMC is just a “soldered” SD-Card (with a few boosts in speed and so)
Best,
Simon
That looks really cool and definitely practical! 
I’ve seen some alternative boards, like UPS PIco (though this one is out of stock), and feels like if I have a more serious project myself, would definitely need one. 
After some search I’ve also seen SafePi as well. Out of stock too, nevertheless it’s open source design, so can be more future-proof.
That’s a good point about the SD card and eMMC, dug into that a bit more, it’s fascinating still.