Grammarly - Clear, effective, mistake-free writing everywhere you type.
Novelize - Novelize is an online novel writing app designed to keep authors on track.
Hunspell - Hunspell is the spell checker of LibreOffice, OpenOffice.
Manuskript - Open-source tool for writers.
DSpellCheck - Yet Another Notepad++ Spell-checking Plug-In
BlankPage - Stay motivated to write, and finish your story