... with no need to install any software in your computer. That is an advantage if you have a computer with low resources and even if you don't have a computer and still want to start your own software business or project because you have the chance to go to a cyber cafe and write your code from there. A few days ago I had no Internet connection at home and needed to publish some changes to my live system and I went to a cyber cafe and thanks to Cloud9 I was able to accomplish my goal.
Actually I discovered this IDE because I was interested in Ruby On Rails but since it is based on Ruby there was not much support for development environments for Windows. After some research I discovered that there was a place where you can have a linux instance on the cloud and on top of that have the IDE web interface. That was at the first days I think of Cloud9 at 2009 or 2010 if I remember correctly. I wasn't able to use it back but 18 months ago I looked again into it and created my account and have used it since then.
This IDE offers me as well the chance to install any data base management system since I have a linux instance at my disposal and at the same time Git already installed. Apart from that I can install Heroku tool-belt in order to deploy my application.