Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
TeXworks - The TeXworks project is an effort to build a simple TeX front-end program (working environment)...
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
Archimedes - Archimedes is a LaTeX and Markdown editor designed to make mathematical writing easy.
JabRef - Graphical Java application for managing bibtex (. bib) databases.‎JabRef · ‎JabRef Help · ‎JabRef | Blog · ‎OpenOffice/LibreOffice .