DigiNow's Installable Chrome App My Cloud9, an IDE which lets you connect to any Cloud9 Server, installed locally, remotely, or even Cloud9's hosted servers. This app has been tested and works on Mac, Linux, Windows, and Chome OS!
For those that don't already have their own Cloud9 instance running, or may be having trouble installing it locally or on your server, Brandon Nozaki Miller has documented his process in his installing cloud9 gist.
Use c9.io if you have a username and password by entering c9.io in the hostname field and 80/your-user-name in the port field. This will take you to your dashboard. You can also store all of your c9.io projects by following the step above but enter 80/your-user-name/the-project-name in the port field. If you use a browser you can see the project name in the URL for quick reference to store it in the My Cloud9 app. If you signed up with github or bit bucket just enter your email and hit the forgot password link and C9.io will send you a password so you can log in using your email, username, or sithub/bitbucket account.
When you start the app up enter any information needed to reach your cloud9 installation. The minimum required is the hostname to your cloud9 server. Everything else will default to the placeholder values you see in the input fields if not filled in.