WorldBrains Memex - Bookmarking for the power users of the web. A privacy focused extension to annotate, search and organize what you've seen online.
Diigo - Diigo is a powerful research tool and a knowledge-sharing community
dokieli - dokieli is a distributed article authoring, annotation, and social notification tool which works...
Hypothes.is - Annotate with anyone, anywhere
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Weava - Workspace to highlight, organize & collaborate on your research articles.