There are actually quite a few robust, web-based editors now, including: Cloud 9, Codio, and Codeanywhere.
Originally shared by David Grigg
I hadn’t heard of this before; an open-source HTML and CSS editor, which is itself built in HTML and CSS. Previews in Chrome (updating live as you edit the code). Backed by Adobe. I already like it a lot. What’s more, it’s free!