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.

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

Read, annotate, and share PDFs and more.

Papers helps you collect and curate your research material.

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

A semantic, scientific, web-enabled PDF reader.

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