I've been trying to come up with a good example to demonstrate Topicalla, since I'm not sure if people know exactly what it's supposed to do. There are some screenshots I've made, but I don't think they do a great job of showing what it does. Part of the problem lies in requiring other pieces that just aren't there yet. For instance, a server or set of servers for handling general search queries, and gathering info that is related to a resource, and the framework for editing things.
So far, I've been using RSS and FOAF as simple examples, as well as a simple movie/actor example. The former two I used because many people are familiar with them and there is a large pool of existing RSS and FOAF ready to use. Unfortunately, RSS files aren't very graph-like by themselves so the added value of RDF isn't demonstrated, and I'm not too fond of showing a demo that makes Topicalla look just like another RSS reader. The movie data can be more graph-like, as actors are associated with different movies in various ways. One issue is getting some public domain movie information and pictures, since I think images will make the screenshots look more interesting.
I've been thinking of a number of other ideas though. Family trees are one possibility, which could build upon FOAF. One could start with a list of people, and drag between people to create relationships. Then I could make a query to ask for how many of my enemies have cousins. In fact, with an RDF Schema, only three properties are really needed, gender, childOf and spouseOf (perhaps variants of the last also). The RDF system could determine a cousin by going up two childOf arcs and then down two childOf arcs, ensuring the middle node wasn't the same. They don't have to be familial relationships though, they could be friends, employees or enemies.
I also thought about extending the animals datasource from the XUL tutorial, since animals are already classified into groups such that RDF types and subclassing can be used, despite that the classifications tend to change as new research is done. But I'm sure it's easier to get publicly available photos of various animals to make the screenshots prettier. I could even go to the zoo and take pictures myself. Actually, I went last week which is what inspired the animals example possibility.
I should point out that Topicalla doesn't really have any built-in support for any kind of data. I've written some samples for RSS, FOAF and so on, but the application doesn't have any special handling for them -- the end user can easily replace the samples with a more powerful UI that views RSS.