GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
MkDocs - Project documentation with Markdown.
TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.
Docusaurus - Easy to maintain open source documentation websites
LyX - LyX is a document processor.