Diigo

Diigo is a web-based research and knowledge management tool that allows users to bookmark, highlight, and add sticky notes to web pages and PDFs. It provides features for organizing collected resources, sharing them with groups, and collaborating on content.

Diigo is a comprehensive web annotation and bookmarking tool that directly aligns with all the 'must-have' features. It allows users to save and preview URLs, organize them into a personal library with tags and outlines (lists and sections), add highlights and sticky notes (contextual side notes), and share content publicly or within groups. The platform also supports instant link adding via its browser extension and offers a user profile gateway. It supports various media types, requires sign-in for full functionality, provides granular sharing permissions through groups and public/private settings, and is accessible on mobile devices.