Cloud9 is a web-based Integrated Development Environment a.k.a. IDE, hosted versions of which is provided by Cloud9 itself with various pricing and plans depending on your needs (Including Free plan). Being web-based it is very handy as you can log into it from any machine and get the same Ubuntu based environment including root access. On there platform they offer various images depending on your needs and programming language that you use.
Harvard’s CS50: Introduction to Computer Science course uses Cloud9 so that all students can get same environment to work irrespective of there machine configuration or operating system they are running.
Also, Cloud9 IDE is a free and open-source software, source of which is hosted on Github.
Hosted version is nice but if someone wants to install it locally, I wrote a script in past to make it possible. Based upon the script, I wrote this Docker Container image which is so much easier to use and doesn’t mess things up on the main system as it runs in a separated isolated container of its own.