There is a very simple navigator on the left, a thumbnails view, and a preview area.
As I wrote the application based on Eric's and Tom's work, I started by implementing a couple of views that I contributed to the new e4 Workbench through an extension point.
Then I realized that all I need is an EMF model representing the parts that make up the UI: the views, the menu, and the toolbar. I don't actually need any extension points, because my application is not an extensible IDE - it is a rich client application for which I know how the UI should be structured. I am pretty happy about the end result - my application is fully described by one XMI file that I can edit using an editor for EMF models, and I can just go and modify that file if I want to rearrange views, add new ones, delete unnecessary ones, build my menu structure and so on.
Compare this to how it works with the current 3.x Workbench: I would have to write a perspective extension, a couple of views extensions, a command extension, a menu and a toolbar extension. Then I would have to assign unique IDs to all these pieces, and to ensure that IDs match up properly. How many hours we've wasted in the past when IDs did not match up!
Of course, this only works for closed applications, not for open and extensible ones like e.g. the Eclipse IDE. However, it is still pretty useful to be able to reason about a concrete EMF model representing the UI application structure. For example, when you have lots of little pieces contributed by many plug-ins, we can now talk about what it means to produce that concrete model from the many little pieces. One interesting question based on this is: Can we maybe generalize the many ad-hoc mechanisms we have grown over the last years (most of which involve matching up IDs) to something that is less ad-hoc and more general?
It's been fun to work on this little application so far. If you would like to participate, let us know on the e4 mailing list, and/or attend the bi-weekly e4 conference calls. You can always email me directly, of course.
P.S. The code is available in CVS - check out the ui/demos project under /cvsroot/eclipse/e4-incubator to get the launch configuration and project set file (emf-workbench.psf).