Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.
TypingDNA Authenticator - 2FA codes in your browser, secured by the way you type
Google Authenticator - Google Authenticator is a multifactor app for mobile devices.
Cotter - One-click phone number login and checkout
Duo Security - Duo Security provides cloud-based two-factor authentication. Duo’s technology can be deployed to protect users, data, and applications from breaches, credential theft, and account takeover.
Auth0 - Auth0 is a program for people to get authentication and authorization services for their own business use.