There's also Ethercalc [https://ethercalc.org/], a spreadsheet version of Etherpad.
Etherpad, Ethercalc and Mailpile (and more!) are all available on top of Sandstorm [https://sandstorm.io/apps/] - which basically makes it easier to manage them all.
For writing and other docs, I personally use Dropbox but I know that is not the same as working in the browser itself.