Recs.
Updated
Nitrous gets your project up and running lightning fast. The IDE includes not just a file browser and text editor, but a fully-functioning shell - you can even code in vim or emacs if you prefer - all from within the browser.
Specs
Pros
Pro World Accessible URLs - Preview Your Application
Since you are using a linux box on the internet you are able to expose your apps to the world out of the box.
No messing around with firewalls or NAT. It Just Works.
This is most useful when needing to demonstrate or work on a task with other people who are not on the same LAN as you.
Pro Allows you to edit locally with provided Atom plugin
Nitrous.io recently developed (in open beta) a plugin for Atom called Nitrogen which allows you to work locally within Atom, utilizing all of the features and plugins you enjoy in Atom, as well as having the sync capabilities of their original desktop sync app.
In short, it's brought the power of Atom and it's extensive plugin community to Nitrous's ability to provision and maintain development/production environments all in one package.