Online collaborative writing, citing, hosting of data and publishing.

Google's mission is to organize the world's information and make it universally accessible and useful.

Annotate the web, with anyone, anywhere.

Read, annotate, and share PDFs and more.

Perma.cc is simple, easy to use, and is built and supported by libraries.

Papers helps you collect and curate your research material.

An easy and intuitive way to discover, read, annotate, write and share scientific research.

WorldCat is the world's largest network of library content and services.

A semantic, scientific, web-enabled PDF reader.

Mendeley is a desktop and web program produced by Elsevier for managing and sharing research papers, discovering research data and collaborating online.