Clash of Clans

Clash of Clans is a simple, highly addictive concept - build a town and its defences, then train your troops to fend off attacks from other players. As it's a persistent multiplayer game, its duration is basically never-ending, and is one of the most popular games on the Play Store. Your progress syncs to your Google + account, so you can continue your game across multiple devices.

credit: androidpit.com
https://play.google.com/store/apps/details?id=com.supercell.clashofclans