Readwise - Effortlessly rediscover and organize your Kindle highlights
Klib - Kindle & iBooks Highlights Manager
Clippings.io - Organize the notes you make on your Kindle
Pocket to Kindle (P2K) - Send articles saved in Pocket to your Kindle
Newsletters to Kindle - Read your newsletters on your Kindle
Kindle2Notion - Export your Kindle clippings to a Notion database