Gagdet snaps, the somewhat mysterious part of snappy that few people grok. Being a distinct snap type, next to kernel, os and the most common app types, it gets some special roles. If you are on a classic system like Ubuntu, Debian or Fedora you don't really need or have one yet. Looking at all-snap core devices you will always see one. In fact, each snappy reference platform has one. But where are they?
Up until now the gadget snaps were a bit hard to find. They were out there but you had to have a good amount of luck and twist your tongue at the right angle to find them. That's all changed now. If you look a https://github.com/snapcore you will see a nice, familiar pattern of devicename-gadget. Each repository is dedicated to one device so you will see a gadget snap for Raspberry Pi 2 or Pi 3, for example.
But there's more! Each of those github repositories is linked to a launchpad project that automatically mirrors the git repository, builds the snap and uploads it to the store and publishes the snap to the edge channel!
The work isn't over, as you will see the gadget snaps are mostly in binary form, hand-made to work but still a bit too mysterious. The Canonical Foundations team is working on building them in a way that is friendlier to community and easier to trace back to their source code origins.
If you'd like to learn more about this topic then have a look at the snapd wiki page for gadget snaps.