Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
Write App - No-distraction writing tool for your productivity.
TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.
Hemingway - Hemingway App makes your writing bold and clear.
LyX - LyX is a document processor.
ProWritingAid - For the smarter writer. A grammar checker, style editor, and writing mentor in one package.