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.

Public search engine and digital library for scientific and academic papers.

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.

Reference manager which finds & organize documents and cites research literature

Papers helps you collect and curate your research material.

Citation management software program for Mac and Windows.

Read, annotate, and share PDFs and more.