Writebox is a free, in-browser app for Chrome and web browsers. There is a separate app for iOS and Android (for $1.99 each). Its font and background can be fiddled with, but beyond that it is stripped down, perfectly comprehensible, and works with Dropbox and Google Drive. It understands markdown, and can offer a toggled preview. It offers a word count, and the ability to save as html or email text or html. It does not have navigational aids (bookmarks or jump functions) or the ability to directly print.
Apparently it doesn't work as well on the mobile platform browsers. Once you start typing, the menu options disappear. It has also been reported to struggle with large files (5,000 words or more). But again, there's an advantage to something that stretches across multiple platforms. While it isn't free, it's not expensive, either. I sprung for it.