I've been thinking for a while about an application for mobile devices that knows rail, bus, ferry, and magical flying eagle timetables and stops. The idea is to be able to glance at a mobile device and see it say "hey you are at foobar, its 9pm, I guess you want to go home/to hotel, and here's how you can do it, how regularly that happens and the last time you could do it today".
Of course, n900 guys will want to just use a web service for this. But as mobile data costs kidneys in some parts of the world, I'm more inclined to choose a design that precaches the data when free wifi is available. This also plays well for travelling with roaming charges etc.
If you are travelling, then the machine should already know where you are staying and when, so it can direct you to the metro line of interest from where you are to get there. Again for travelling, being able to wangle a timeline to move "now" forward and see that the app can suggest reasonable options as it goes is also a good idea. You don't want to rely on it to suggest and then find you are late for the jet.
I'm thinking perhaps Qt/Soprano for this, but the exact RDF vocabulary for the bus, train, etc timetables is not jumping out at me. There are many adhoc designs I've thought about, like a series or RDF list of ical entries for each bus run, perhaps with each entry using geo84 or some other ICBM assocation method. If you know of a good RDFS for this, please let me know. I don't know when/if I'll get to hack on the code, but the itch to do so is unlikely to go away by itself.