SoftMaker FreeOffice is a suite of office programs, and one of the included tools is a free word processor called TextMaker.
It runs on Windows, Linux, Mac, and mobile devices ( iOS and Android). Writer is part of the WPS Office software, so you have to download the whole suite to get the Writer portion. You can also add custom dictionaries, read/write to popular file types, create a cover page and table of contents, use built-in templates, encrypt documents, and easily view all the pages of a document from a side pane. There's even a viewing mode to protect against eye damage, turning the background of the page into a greenish color. Writer supports full-screen mode, dual page layout, and the option to hide the menus, which makes for a perfect distraction-free writing experience. You can easily toggle spell check on and off from the menu at the bottom. Spell check is performed automatically as you would expect to be done in a good word processor.
WPS Office (previously called Kingsoft Office) is a suite that includes a word processor, called Writer, that's easy to use because of its tabbed interface, clean design, and uncluttered menu.