AltStore Classic is an alternative app store that lives on your device. You run AltServer on a computer on the same network, and it signs and installs apps using your own Apple ID.
It is for people who want to install open-source apps or their own builds without a paid developer account.
Honest limits: a free Apple ID allows only a few active sideloaded apps and each one must be refreshed every 7 days. We do not host AltStore or any app; use the developer's site.