These free apps can help you get your business right without breaking the bank.

For quick travel math: Amount Plus

I'll never forget being with a colleague overseas on the last day of our travel. She checked the price of a item to bring home to her kids and, after talking to a sales person, she suddenly turned pale in the face. She had been using the wrong currency conversion math - and had spent the week spending about ten times the amount of money she thought she was.

Amount Plus prevents this nightmare from happening. It simply translates any numerical value to another measurement. We're talking meters to miles, cups to quarts or rupies to dollars. The free version is fine, but pony up a few cents for the deluxe version. The compact, easy design makes it perfect for quick situations.

For learning languages: DuoLingo

Unlike other apps, DuoLingo is honest about how you're going to learn a language: Do it every single day. It makes the communication process playful, rewarding you for daily streaks, three ways to learn (reading, listening and speaking) and gamifying the experience. It argues that 34 hours of DuoLingo equals a university semester of language - a tall order, but it doesn't diminish the effectiveness of the app itself.

It is also completely free and ad-free, too. It's worth listening to DuoLingo co-founder Luis von Ahn on the Tim Ferriss Show on the history behind the app.

For planning: Hopper

There are dozens of travel-planning apps and Hopper stands out because it is ridiculously simple. Open the app and type in your to and from airports.  You get a color-coded calendar based on price ranges for each day. Pick a day to get the flight options.

The killer trait is the watching ability: Pick a flight and Hopper will shoot you a phone notification when it is the best time to buy. Unlike Kayak and other platforms, Hopper uses billions of statistics to predict when flight prices are their best. It has already saved me significant money this year - and, with the push notifications, it was a completely passive experience.