I only disliked one thing.. I couldn't install yeoman for scaffolding some apps.. I don't know why! I'll need more research...
Thanks :)
The others I've heard of are Koding (https://koding.com/features/solo#get-started), Codio (https://codio.com), and Runnable (https://runnable.io/, doesn't appear to be an IDE).
I use it to code C++. It's nowhere near the levels of VS2015, obviously, but it allows me to have a free dev box in the cloud.
The only issue is that c9 seems more suited for web development.