If you're one of the growing number of converts to writing in Markdown you might be interested in a new Chrome Web App called TextDown. While there have been other Chrome-based text editors (for example, WordFlow), TextDown adds a live Markdown preview, letting you see how your text will look when it's rendered as HTML. It also includes some useful features like the ability to save and open local .md files, add images, get a word count and elapsed time, and of course export to HTML. The app, designed by João Colombo, lets you copy nicely formatted Markdown links from the browser's right-click menu, too; a great feature to have even if you never actually write in TextDown.
If you're not familiar with Markdown, at its most basic it's a formatting syntax that lets you write documents in readable plain text and quickly generate HTML, but there's a lot more lurking beneath the surface. As Brett Terpstra notes, TextDown is still very much a beta, but it's definitely an interesting idea, and free to try out from the Chrome Web Store.