iTunes 
Automatically download new iTunes Store purchases to multiple computers and devices
When you purchase items in the iTunes Store, you can have them downloaded automatically to multiple computers and devices. This way, all your computers and devices have the same new content, even if you don’t sync them.
You can turn on automatic downloads on a total of up to ten devices and computers, combined. You can authorize up to five computers at a time with an Apple ID.
Note: Some items may not be available for automatic downloading in all countries.
Turn on automatic downloads on an authorized computer
In iTunes, choose iTunes > Preferences, and click Store.
Below Automatic Downloads, select the types of content (Music, Apps, and Books) you want to download automatically.
If you’re using Mac OS X v10.6.7 or later, and iTunes is open when you make a purchase on another device or computer, the purchased item downloads to your computer at the same time that it downloads to the other device.
If iTunes isn’t open at the time of purchase, or if you’re using Mac OS X v10.6.6 or earlier, the item downloads automatically the next time you open iTunes, or when you choose Store > Check for Available Downloads.
Turn on automatic downloads on your iPod touch, iPhone, or iPad
Important: Before turning on automatic downloads on an iOS device, make sure you’ve signed in to the iTunes Store on the device.
On your device’s Home screen, tap Settings, and tap iTunes & App Stores.
Tap to turn on each type of content (Music, Apps, and Books) you want to download automatically.