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The AltStore is an alternative to the App Store on iOS giving you many new possibilities for your iPhone. It allows you to sideload any IPA app that you have downloaded from the internet that isn't normally available in the regular App Store. Unc0ver is a jailbreak, which means that you can have the freedom to do to whatever you want and operate within your iOS device. It is considered one of the safest and easiest to use jailbreaks available to use on iOS devices.