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

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

Annotate the web, with anyone, anywhere.

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

Read, annotate, and share PDFs and more.

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

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

Papers helps you collect and curate your research material.

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

A semantic, scientific, web-enabled PDF reader.