Aegis Authenticator

Aegis is the one to pick if you are on Android and want your 2FA codes stored encrypted and backed up under your own control, with no cloud account in the loop. The flip side of offline-only is that moving to a new phone is a manual export-and-import you have to remember to do, and there is no iOS version at all. For Android users who want open-source, encrypted, account-free authentication, it is the standout choice.