Pocket Planes is a sim game in which you get to run an airline company, dealing with the tasks of routing planes to maximise profit and deciding how best to allocate your funds in acquiring new planes vs opening new routes.
The game is brought to us by the same developer as Tiny Tower and shares some of the latter's features: a 'retro' graphics style and an in-game economy based around normal and premium currencies.
The game's strategy revolves around selecting available "jobs" (people or cargo needing to be flown to a particular airport) and allocating them to planes depending on their capacity and location: for example, whether to take on a longer flight for potentially more profit or a series of shorter runs with a given plane. Passengers may be unloaded at airports mid-route and such "layovers" coming from different starting points can then be combined, for example, into one more efficient flight on a larger plane to their final destination. You start the game with a small number of low-capacity planes and must gradually acquire higher capacity, higher-range planes as you expand your available airports. Another element of strategy is therefore deciding how to invest your funds (expansion of available plane slots or expansion of your airport network).
The game is quite fun and addictive overall and features more strategy than its aforementioned sister app Tiny Tower. An aspect that is slightly confusing is that purchase of planes evolves around a constantly changing "marketplace", occasionally making it difficult to "save up" currency for a particular acquisition only to find that it has disappeared from the market.
If you're into sim games and don't mind the retro graphics style, then you should definitely check out Pocket Planes.