Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.

Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.

TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.

Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.

LyX - LyX is a document processor.

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.