WhatsApp and other handy travel apps

These are the Apps which may save you headaches and/or time while you are traveling.

WhatsApp Messenger 

A cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android, Windows Phone and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.
Please check with your own mobile service provider for travel overseas mobile plans.

Currency Converter

I use XE Currency.  Place Hungary, Austria, & Czech Republic on your main screen for this trip, and shake your phone for real-time updates.
Need to calculate currencies on-the-go? With the XE Currency App, you can access live exchange rates, view historical charts, and calculate prices on your smartphone or tablet. With over 25 million downloads worldwide, this FREE app is available for iPhone, iPad, Android, BlackBerry, Windows, and Firefox OS devices.

Your Airline's Mobile Site

This will allow you to check flight status, gate arrivals, etc.

Your Stopover City App

I am trying out ParisGo, a free app with great reviews.
ParisGo can view the next passage of
Subway, bus, RER, Transiliens, Noctiliens, Trams
at the station of your choice.
Different maps of metro / RER can be downloaded from the application.

Smart Layover

Normally, layovers are no fun; we all know this. So instead of avoiding your next layover, plan for it with Smart Layover and turn your layover into an adventure. Smart Layover offers a unique user friendly mobile travel app for iPhone, Android and Blackberry. If you have a layover (or worse, a missed or delayed flight), the Smart Layover app will hook you up with some great layover activities.