This looks like a pretty cool Chrome Extension. Similar to programs live Scrivener, from what I can tell. Exports to .epub and .mobi, among other formats:
https://chrome.google.com/webstore/...source=en-et-na-us-oc-webstrext&utm_medium=et
https://chrome.google.com/webstore/...source=en-et-na-us-oc-webstrext&utm_medium=et