I travel a lot with friends, and I have two apps that I don't leave home without:
This app lets you track costs between friends while on your trip. Whether it is paying for hotels, meals out, drinks at the pub, this is the easiest way I have found to track costs and then easily settle it at the end of the trip.
Relivit lets you take 1 second videos of your trip, and then merge them together into an action packed video that you can use to show off your trip on social media, or directly with friends. It is like a similar app "1 Second Everyday" but is free to download and use.
I agree that travel apps have a long way to go, i love the idea of easily being able to find itineraries for what to do in certain cities / towns / regions. Do any apps exist that do that?