Two-Factor Authentication
A password isn’t enough and even the most unique password can be leaked and discovered by bad actors. Two-factor authentication (2FA) offers another level of protection by using an app to deliver you an always changing, timed code to use once you enter your password.
A note of caution: if a website offers 2FA, always choose the option to use either an app or even a hardware key, but avoid SMS. While SMS is still better than no 2FA, SMS messages can be intercepted and are not as secure.
Use Instead Of: Google Authenticator, Microsoft Authenticator.

Raivo OTP
A native, lightweight and secure time-based (TOTP) & counter-based (HOTP) password client built for iOS

Aegis Authenticator
Aegis Authenticator is a free, secure and open source app for Android to manage your 2-step verification tokens for your online services.