Well yes there is more so for those who like to explore collaborative tools here are my latest finds:

Twiddla is a collaborative space that includes a host of tools:
Whiteboard, chat, draw tools, file sharing and much more.
The best thing about Twiddla is that your invited people don’t have to log in anything and you can begin to work immediately.
Does it work on mobile devices? Only partially, the text tool for example does not work, but you can still draw, copy and paste, chat, etc
As not all tools will work on mobile devices, test activities you would like to do with your students before the lesson if you are going to have them using iPhones, iPads, etc. To start Twiddla click here

Read more about Twiddla here or watch this YouTube video for an introduction
Click here for video

Another great collaborative space is Nota - Latest!!!! Nota is no longer available and that is a real shame as it had some real potentials (11th May 2012)

Again this is a tool for collaboration in the clouds and aside some of the features of others collaborative spaces it allows you to embed videos, use a webcam (although as far as I can tell there is no sound), etc.
Like Twiddla, easy to use, set up and go.
To explore Nota click here
Does it work on mobile devices? Not very well the text tool for example will not work so, as for Twiddla, test it first to see if the activity you would like done on a mobile device is doable before suggesting it to your students.

More on collaborative tools I love and you should check out

Padlet and Flipgrid