Feeder.mobi is a simple web service built upon WordPress & BuddyPress, that lets you subscribe to RSS / Atom feeds and have them sent daily / weekly to your Amazon Kindle device as a mobi EPUB file.
No Ads, No Tracking and No Fees!
For now it is free to register but it is under heavy development. If you want to help me out or report some issues, the project is hosted on Github.