You heard it folks at the Bethesda E3 concert along with Fallout 4 a new mobile app named, "Fallout Shelter" was announced. The app is currently available for download RIGHT NOW on iOS.
This app will allow you to be the overseer over your very own custom vault. You can manage the Vault Dwellers to keep them in high spirits and send them out to scavenge for supplies. You can also breed them and defend your vault from internal and external threats like, radroach attacks, vault malfunctions, and raider attacks. You can collect special lunch boxes to win prizes and items to supply your vault. This app is FREE to download and there is no "freemium" elements. The only thing you'd need to sink your money into is the special lunchboxes to get a little extra supplies every once in a while.
Once again this is free to play and download, and available now on iOS. The Android release is sadly a bit late, but hopefully they release it soon.