About images of the UI: Fossil's website is run by Fossil, so you are, in fact, looking at Fossil's UI when you visit TFA.
But more importantly, things like side-by-side screenshots of Gitlab / Github / Fossil of major features will also be immensely helpful. I'm thinking of things like pull requests, ticket trackers, ect.
You may find the article of some interest, since it summarizes one common use case for Fossil.