Trainyard (4.5/5 stars, all ages, FREE today only) is today’s Amazon Free App of the Day, and it’s from the wonderful developers at Noodlecake Studios. From Amazon:
Trainyard is a puzzle solving game unlike any that you’ve ever played. It’s easy to learn but very tough to master. Your job is simple: get each train to a goal station. Red trains go to red stations, blue trains go to blue stations, etc. You control the trains by drawing track for them to follow. There isn’t a time limit or even a score; the only thing you need to do is figure out a solution for each puzzle.
The first few puzzles are almost too easy, but as the difficulty increases you’ll be thankful that you were able to practice the fundamentals of drawing track. As the game progresses, you’ll have to use colour theory to combine trains of different colours, use timing to merge and split trains, and use every inch of your brain in your quest to beat the game.