Readwise - Effortlessly rediscover and organize your Kindle highlights
Pocket to Kindle (P2K) - Send articles saved in Pocket to your Kindle
Clippings.io - Organize the notes you make on your Kindle
PocketRocket - One article from Pocket to your Inbox everyday
Klib - Kindle & iBooks Highlights Manager
Nimbooks - Host all your digital reads in one place