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.
Highlight - "Highlight" physical books through conductive pages 📖✨
Diigo - Diigo is a powerful research tool and a knowledge-sharing community
Weava - Workspace to highlight, organize & collaborate on your research articles.
Quotle - Save, share & discover text from your mobile
Sumnotes - Export highlights from PDFs