YubiKey - The YubiKey is a one-time password device for secure login with two-factor authentication
Aegis Authenticator - Aegis Authenticator is a free, secure and open source app to manage your 2-step verification tokens...
2FA Authenticator - Simple 2FA Authenticator - Generate Two Factor Authentication tokens.
Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.
U2F Zero - A secure and open source 2 factor authentication token. Designed to be affordable and reliable.
Google Authenticator - Google Authenticator is a multifactor app for mobile devices.