Please share more. I have two Kindle 3 laying around and I'd love to do something useful with them. Everything I read about hacking older Kindles involved root

Please share more. I have two Kindle 3 laying around and I'd love to do something useful with them. Everything I read about hacking older Kindles involved rooting them and displaying a HTML with whatever you wanted. That sounds too easy, and I'd like to go deeper.