Take a glance at the top free game charts for the iOS App Store, and you'll spot that a little game called Merge Plane is doing rather well for itself, both in the US and the UK.
Curious sort that I am, I downloaded the game and gave it a quick spin. It's a reasonably compelling idle clicker with - as the name suggests - a 'merge' mechanic at its core.
This means combining two core items to make a single upgraded item - and repeating ad infinitum.
In the case of Merge Plane, this gives you better and better aeroplanes that you can then put to work earning your airline a living.
Like I said, it's pretty good fun, in a limited sort of way. But if you like Merge Plane, you're going to take off when you play these five games.