Hello Travelers,
I want to start this topic to gather different opinions on - what apps are useful for travelers and especially for those who travel by air.
I think this one pretty useful – Alarm Travel Clock Pro
http://www.alarmtravel.com
I’ve used it a couple of time and pretty satisfied with it.

Write down what apps are you using while traveling.

I've found that the built in alarm clock is fine for me.

Based on very recent experience, here are some handy apps to have.

- Kayak
- Airline you are flying, and your FF/ login info already set up
- Rental cars - more than one, with your membership and discount info already set up. Hertz app sucks - it was much easier to call them up.

I have the following Apps:

FlightTrack
GateGuru
TripIt
TripAssist
FlightGuru
Kayak
Travelocity
Expedia

Plus apps for many of the major hotel chains, several car rental agencies, the airlines I frequently fly and apps like Open Table, Yelp and Translator.

I use some apps more than others but they are there if I need them.

Not exactly "travel" related apps but I also use XE Currency Exchange and a weather app.

Not sure there's a need the AlarmTravel App mentioned by OP. There's a built in alarm on my phone and there's always the option to get a "Wake Up call at any hotel - so what's the point?

I have FlightAware (Iphone) which I love. Lets me track any airline flight.

I also use Oanda Currency Convertor.

FlightAware is my favorite, too