I’ve also came across very different projects where I used Kirby (v1 and v2) or at least the old toolkit.
Besides the normal corporate websites (check out http://hpz-scharnhausen.de, http://volt-gear.com, http://ruderclub-nuertingen.de, http://zetb.de – and some very interesting sites are still work-in-progress), I also worked on quite complex web applications for managing different types of data – a order management tool for volt-gear.com (orders in a database, but the tool itself is an own kirby installation), a customer/calendar/invoice tool for hpz-scharnhausen.de, and some small, easy installations for a custom wiki for example. Maybe I will build some edited screenshots with dummy data and more detailed description, if you’re interested 
I think pretty much any app/website can be build with or on top of Kirby. I just came across http://bastianallgeier.com/openzoo/ again, and thought that also a bookmarking tool would be easy to set up with kirby… maybe my next project in free-time…
Oh, and another old project from @bastianallgeier inspired me for building an easy project-management-tool: https://github.com/bastianallgeier/gantti – have to get some more freetime 