For modern travel apps, intermodality is an important feature. That is to say, the traveler is being guided seamlessly from his home to his hotel at the destination (door-to-door-navigation) using bike, public transport or car. The app can even offer real time information about delays and changes and shops/restaurants nearby.
Travel apps can be connected to external systems which for example help finding a parking space or a rental car and enable shopping on the go. Location based services, which are interesting for retailers at train stations and airports, can be integrated.