Readwise - Effortlessly rediscover and organize your Kindle highlights
Hacker News Stack - Focus on the really fresh and unread news in Hacker News.
Clippings.io - Organize the notes you make on your Kindle
Hacker Newsletter - Best of Hacker News in your inbox every Friday.
Klib - Kindle & iBooks Highlights Manager
Hacker News Front Page Explorer - A database of top ranking Hacker News front page posts