Cosmic Express is a puzzle alien train themed game. Each level is something like an 8 x 10 grid and a space can be empty or contain an object:

* Entrance - there is one entrance where your train comes in
* Exit - there is one, sometimes two, exists where your train must leave
* Obstacle - can't build on
* Passenger - need to pick these up
* Destination - need to deliver a passenger to the same colored destination
* Hole - teleportation hole that teleports to another hole

And probably more as I've only done about 80 levels.

You lay one continuous track from the entrance to an exit. Your train must eventually pick up every passenger and deliver each to their destination. It's usually something like two groups of different colored passengers which must be delivered to two groups of different colored destinations and your train can carry one to three passengers (depending on the level).

So there is a lot of winding around to make sure you pick up and drop off passengers in the right order and taking advantages of quirks (e.g. if two passengers try to board the same car at the same time then they bounce off each other). It's basically a 2D pathing game with hundreds of levels. Cute graphics and sounds and fairly easy UI since it's designed for mobile.