Apache OpenOffice Writer - Open-source word processor of the Apache OpenOffice suite.
JotterPad - JotterPad Writer for Android — Turn your thoughts into text. Go about your creative writing without distractions, write to your hearts content...
LibreOffice - Writer - Open-source cross-platform word processor.
Polar Word 2020 - Polar Word 2020 is a powerfull word porcessing software !
YourQuote - YourQuote is an interactive mobile app that helps you to write stories, quotes, screenplays, poems, and 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.