I really hope that the Cloud9 service keeps running, and maintains the free version that it currently provides. I have been using Cloud9 with the Michael Hartl Rails Tutorial to teach new programmers the basics of programming with Ruby and Rails and it has greatly reduced the friction for them to start learning.
In previous classes we had the students setup a Ruby and Rails environment on their own systems and not only did that take multiple sessions to get setup, but then we were dealing with environment differences that took the focus away from the basics of learning Ruby nearly every session.
Wouldn't virtual machine basically do the same thing? I've taken some classes where teacher gave us an image where everything was already installed and configured. Everything went smoothly.
However, Cloud9 is much more convenient since it runs entirely on browser but VM solution could work in case C9 discontinues its free tier.
One of these days we'll have fast enough Internet speeds in the U.S. that remote VMs will work (nicely). We're definitely not there yet.
The nicest thing about Cloud9 is being open source you can install it on your own hardware so those VMs don't have to be remote.
Unless something has changed since last year, it is not truly "open source" if you're going by the Open Source Initiative's definition of "open source".
Evidently there are a number of restrictions placed on the source code that prevent this from being the case. There was a Reddit discussion about it at the time:
https://www.reddit.com/r/programming/comments/2vvs7i/cloud9_...
It is most definitely open source it is just not unconditional, maybe that will change now.