The web and hand-held-device writing app My Writing Spot (once called My Writing Nook, until B&N got proprietary about the word "Nook", which is idiotic, since nobody would confuse the the writing app with the ereader device) has had some nice updates to the web part, including: change of font and text size.
On a computer the lack of this feature was less important, but Safari on iPad/iPhone and the browser on Android can’t change text size. (Which by the way I consider a glaring and shameful flaw, since you need this feature more the smaller the screen is.)
There are many very good writing apps on iOS now, but My Writing Spot were the first and only one (apart from Pages) I found on Day One of the iPad era, so I still have a weak spot for it. So far as I know, it's also the only one with a simple web browser interface included, so you can write on any web-enabled device or computer in the world, I think that's powerful.
This is the web interface, but MWS also has dedicated apps for iOS and Android.
It is text-only, no formatting. But I prefer that when I'm writing, and just to indicate the little formatting I need in Markdown, like one asterisk for italics and two for bold.
MWS uses Google's authentication system to save the documents, so you need to have a google account (but not necessarily a Google email address).