I recently purchased a Kindle to restart my interest in reading and of course the first thing I did was to figure out how to develop my own software for it.
It turns out that the Kindle runs an embedded version of Java without a GC. This seems to have stifled the development quite a bit, so it's really cool to see how Raspberry-Pi/Inky homebrew is becoming a thing.
There's software which can be side-loaded on Kindles (and Kobos etc.), e.g. Koreader, written in Lua: https://github.com/koreader/koreader