I modified and ported the Calibre to run on GAE two months ago, the web application can aggregate RSS to generate a MOBI file with images, then deliver to your kindle automatically.
The KindleEar is open source application, source code hosted in github:
https://github.com/cdhigh/KindleEar
My website:
https://kindleear.appspot.com/
or you can refer to FAQ for much information firstly:
http://kindleear.appspot.com/static/faq_en.html