You start underground with a pickaxe and a rock. Hitting the rock drops ore, ore buys a better pickaxe, the better pickaxe gets you through to the next depth, and for the first few minutes that is the entire game. Then a second tab lights up along the side, and a third, and the mine turns out to have been the tutorial.
What it becomes is a dozen small games sharing one save: a village handing out jobs, a horde you send into a dungeon over and over, a farm you plant on a grid, a gallery, a card collection. Each has its own currency and its own reset, and the resets pay out into the others, so the mine you abandoned an hour ago is quietly funding the farm. There is no ending to reach. There is a very long way down.