Diamond Digger is my favorite to play on their Royal Games website, so I was really excited to see they've made a nearly identical one for mobile. https://itunes.apple.com/us/app/diamond-digger-saga/id636511657?mt=8 Basically, you're in a tunnel with all these diamonds everywhere. The goal is to make a path to the bottom by matching groups of them. The catch is that you only get 20 or so moves to do so. Once you reach the end, you start a new level, and it keeps going. In the mobile version, they have goals and use the star system. You can't dig more than 9 levels either (so I'm seeing so far). Stars gained are based on how many moves are left and if you've exceeded the goal. There is IAP, but it's really a game about whether or not you can efficiently get to the bottom with precise planning of your moves. I highly recommend it, especially if you don't like any of their other games!