Apple allows anyone to sign apps for personal use with an Apple ID, to let people experiment with app development before signing up for a dev account. If you ha

Apple allows anyone to sign apps for personal use with an Apple ID, to let people experiment with app development before signing up for a dev account. If you have a paid developer account, the ad-hoc signature lasts a year, otherwise it expires after seven days. AltStore runs a server process that re-signs the app before it expires and uses iTunes / Finder to sync the new copy to the device. With a non-developer account, this needs to happen at least once a week to prevent apps from expiring.