TypingDNA Authenticator - 2FA codes in your browser, secured by the way you type
Cotter - One-click phone number login and checkout
LoginRadius Authentication - Secure and robust authentication, SSO with user management
Feather Auth - Build an entire sign-in flow in 5 minutes or less.
Authorizer - Authorizer is an open-source authentication and authorization solution for your applications.
Authpack - Complete user auth system installed with 8 lines of code.