We recommend Google Authenticator for generating time-based one-time passwords, but any TOTP compatible app should work. 

Other apps we have tested include Microsoft Authenticator and FreeOTP.

The process for adding Cryptal to any TOTP app is the same:
1. Enable TOTP Authentication in your Cryptal profile
2. Open your TOTP app on your mobile phone
3. Click add (+) and scan in the QR code (or enter the secret key) to create your account in your app
4. Enter the passcode shown in the app to add it to Cryptal