I like the idea of showing the progress of an application over time. You could use your CI system to take a snapshot on every commit. In the simplest form you could just take a screenshot, or to capture interaction you could record selenium tests (or any equivalent suite).
Just went back through the Git history, found milestones and checked out those commits. Ran each commit in the sim and took a video. First time I have done that and pretty happy with how it turned out :).
