Thanks for you answers. I thought a Kindlet was something different to an Applet (not just signed, but another superclass), because of this:
https://kdk-javadocs.s3.amazonaws.com/2.0/index.html
Do I need to implement this interface?
I've downloaded the merged keystore, put it at /var/local/java/keystore/developer.keystore, then downloaded Endless Book of Sudoku, Kalculator, and KindletChineseChess. They appear on the main menu when I put them into the documents folder (aha), however I can't run them, all of them produce an error saying 'The item you attempted to open is incompatible with this Kindle. blahblah' -> Is this because they don't support Kindle Touch, or did I do something wrong?
OK, now I'm off doing my homework

meaning reading the How to write Kindlets guide. Cheers