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.