SageMathCloud is a completely new thing, which is much more comprehensive than either the IPython notebook or the previous Sage notebook. It provides the ability to run arbitrary services and connect to them, and provides a very easy way to launch an IPython notebook server. Log in, create a project, click "New", and then click "IPython notebook". It starts up an IPython notebook server (patched to allow collaborative editing) and tunnels the connection out so that you are interacting with the IPython notebook server it started up. Beyond that, it has a completely new Sage notebook, terminal, latex editor (all allowing real-time collaboration), automatic snapshots every few minutes, and many more things.