Kalypso Media is a German video game developer and publisher. They mostly make simulation games, like the Tropico series. Their games tend not to be the highest rated, but they do okay, and what they lack in blockbusters they make up in number of different games released. And apparently they also make a handful of mobile games, one of which is Airline Tycoon Free Flight.

Airline Tycoon Free Flight (ATFF) is a business simulation game, which for mobile has been reduced in complexity compared with Airline Tycoon 2 or other PC business simulation games. The most important deviation from more serious business simulations is that in ATFF you can't make a loss on a flight; if the cost of a flight is higher than its revenue, you simply get 0$. Which makes the game very casual, which isn't necessarily a bad feature for a mobile game.

The basic game consists from flying passengers from one airport to another, on a world map which is flat, not round, and so there is no connection from Asia to America. At the start you only have access to small airplanes, cheap staff, and few airports. So you make money on those flights and invest that money in more and bigger airplanes, more and better staff, and more airports, which you can also upgrade to hold more passengers.

The passengers arrive at the airports in real time. So if you played for a while, you will run out of passengers, and better stop until the airports are full again. Other than that there is no artificial energy / stamina resource that prevents you from playing as much as you want. And once you got enough airports and have the upgraded, you can play for quite a while before you run out of passengers. Also in other aspects the game is unusually unobtrusive for a Free2Play game: At no point does the game present you with a pay wall, or nag you for money. There is a currency you can buy for cash, but it is not really needed for anything but a few special airplanes and staff members.

While ATFF is certainly harmless for a business simulation, it is actually quite fun to fly airplanes left and right and try to improve your network of airports. I would recommend trying out the game for free.