Readwise

 Readwise  is a paid web app/service that allows users to sync highlights from various web and digital sources and review them (using spaced repetition) via an app or daily email.

Features
Highlight sync support is available for Amazon Kindle, Instapaper, Pocket, and iBooks.

Their UI will also allow one to tag, annotate, search, and organize content.


 * https://twitter.com/readwiseio apparently also allows you to save individual tweets by replying to a tweet with "@readwiseio save" which then replies to you with "Done! We've saved this tweet to your library so you can revisit/remember it" and some stats like number of times that tweet was saved, and both unique & all saved tweets from that author


 * Readwise also supports unrolling a tweetstorm and saving a copy of it: https://twitter.com/readwiseio/status/1309209103475056640
 * "Done! We've saved this whole thread to your library so you can revisit/remember it 🧠📚 Stats: • 4 saves of this thread (ranked #444) • 1 unique save of mozilla's threads (ranked #1078) • 4 total saves of mozilla's threads (ranked #509)" @readwiseio September 24, 2020

Export
The service provides highlight sync/export to note-taking tools Evernote, Notion, and Roam Research.