A free program for Android, by BinaryBoot.

TOTP Authenticator is a free and open-source app that makes it easy to add 2-factor authentication (2FA) to your mobile accounts. It adds an extra layer of security to your account by requiring both a password and a code (also referred to as a one-time password) to log in. The app is extremely easy to use and does not require any complex knowledge to set up and use. How can I use it? Just install the app and you’re ready to set up and use 2FA on your accounts. You will be guided step-by-step, and the app will automatically start the 2FA procedure for you.