Writing tools

Reference managers

ACS ChemWorx – Collaborative reference manager coupled with tools and services for authors.
CitationStyles – Find and edit CSL citation styles.
Citavi - Reference management, knowledge organization, and task planning solution.
CiteUlike – Search, organize, and share scholarly papers.
Colwiz – Create citations and bibliography and set up your research groups on the cloud to share files and references.
EndNote – Software tool for publishing and managing bibliographies, citations and references
Mendeley – A unique platform comprising a social network, reference manager, article visualization tools.
Paperpile – No-fuss reference management for the web (Google docs plugin). (blog post)
Zotero – Helps you collect, organize, cite, and share your research sources

ASCII doctor – Text processor & publishing toolchain for converting AsciiDoc to HTML5, DocBook & more.
Atlas – Write, collaborate, design and publish on a single platform.
Authorea – Platform to write scientific, academic, and technical documents in collaboration. (blog post)
Draft – Version control and collaboration to improve your writing.
Fidus Writer – Online collaborative editor especially made for academics who need to use citations and/or formulas.
Penflip – Collaborative writing and version control. (blog post)
Pensoft Writing Tool - Collaborative authoring, reviewing and publishing in one place.
ShareLaTex – Collaborative on-line editor for for Maths or Sciences.
WriteLaTex – Online collaborative LaTeX editor.
Stackedit – Markdown editor based on PageDown, the Markdown library used by Stack Overflow.
Typewrite – A simple, real-time collaborative writing environment.
Poetica – Get clear feedback, wherever you're writing.
Quip – Combines chat, documents, spreadsheets, checklist, and more to collaborate on any device.

Writefull – Provides feedback on your writing using data from the Google Books database. (blog post)