Vertigo has a very cool WPF application called Family.Show which exploits many of the new WPF features (data binding, sexy visualization, styles, templates, animation, etc.) and is a good example of the new "Web + Desktop" app hybrids combining the advantages of both paradigms. Family.Show is a genealogy application that you can use to build your family tree. The timeline implementation is very cool and you can "speed or slow down" time and see how your family tree (or forest) grows.
Vertigo has also posted a 5 minute video if you want to see how it works. You can of course save the data in it's native format but you can also import and export it to GEDCOM using which you can use other genealogy programs.