Diigo - Diigo is a powerful research tool and a knowledge-sharing community
Liner - Put simply, Liner is a virtual highlighter. It works on PDFs and webpages in the same way a regular highlighter works on books and magazine clippings. Read more about Liner.
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
Highly for iOS - Medium-style highlighting in every app and website. 🖌
LIBRARIAN - Comment on any arXiv paper
Quotle - Save, share & discover text from your mobile