Subway systems are a fragile, finicky, frustrating, yet vital part of a city's ecosystem, and you'll never feel that more acutely than with Mini Metro. It's not so much a subway simulator as a subway map simulator: drag your brightly colored lines around to connect an ever-growing series of neighborhoods and watch the tiny passengers come and go, slowly getting agitated as your public transit system grinds towards its inevitable collapse.
If you're a regular subway rider, you find yourself accidentally or deliberately copying things you've seen on maps. Will a big ring around the whole system work? Should you try to make a transfer hub in the center? There's a sense of satisfaction when you come up with something that looks like your hometown.
The current version of Mini Metro, which can be installed on Mac OS, Windows, and Linux or played in a browser, is an alpha. The dragging system can be frustrating, and it's not all that clear what the rules are (there are a finite number of tunnels, for example) until you've played around a little. It's still a lot of fun. The full game is set to come to desktop and iPad sometime in mid-2014, and it's currently petitioning for acceptance on Steam Greenlight.