AltServer

AltServer is a companion application for AltStore. The tool runs behind the scenes in your task manager and its job is to make sure that the signing authority of your sideloaded apps is refreshed within the 7 day grace period that Apple allows for free devices.

AltServer and AltStore stay in sync over your WiFi network and AltServer periodically checks to see if it can find your phone. When it does, AltServer sends new signing authority to it, which extends the life of the apps you’ve installed in the App Store.