Bandai Namco have officially launched Dragonball Z: Dokkan Battle on iOS and Android smartphones today. Below is a story summary provided by Namco..
“The story begins when Trunks’ Time Machine crash-lands on a planet where the Dragon Ball timeline has been thrown into chaos! Who could be behind this sinister turn of events? Work together with Trunks to get to the bottom of this mystery, battling legions of familiar foes along the way. The very fate of the Dragon Ball universe rests on your shoulders!”
Dragonball Z: Dokkan Battle is Free, but includes microtransactions.