Doxygen - Generate documentation from source code
Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
Docsify.js - A magical documentation site generator.
TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
LyX - LyX is a document processor.