YubiKey - The YubiKey is a one-time password device for secure login with two-factor authentication
Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.
2FA Authenticator - Simple 2FA Authenticator - Generate Two Factor Authentication tokens.
Google Authenticator - Google Authenticator is a multifactor app for mobile devices.
U2F Zero - A secure and open source 2 factor authentication token. Designed to be affordable and reliable.
Microsoft Authenticator - One app to quickly and securely verify your identity online, for all of your accounts.