Google Titan - A 2FA device to protect yourself from hackers
Cotter - One-click phone number login and checkout
SuperTokens - Open Source User Authentication - An Alternative to Auth0 / Firebase Auth / AWS Cognito
Authorizer - Authorizer is an open-source authentication and authorization solution for your applications.
Amazon Cognito - Amazon Cognito lets you add user sign-up, sign-in, and access control to your web and mobile apps quickly and easily. It scales to millions of users and supports sign-in with social identity providers and enterprise identity providers via SAML 2.0.
Rapid 2FA - A painless way to add two-factor authentication to your site