Pocket to Kindle (P2K) - Send articles saved in Pocket to your Kindle
Readwise - Effortlessly rediscover and organize your Kindle highlights
Knotes - An efficient, beautiful Kindle highlights & notes manager
Nimbooks - Host all your digital reads in one place
Clippings.io - Organize the notes you make on your Kindle
Stash.ai - AI-powered, cross-device bookmarking