Cotter - One-click phone number login and checkout
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.
SuperTokens - Open Source User Authentication - An Alternative to Auth0 / Firebase Auth / AWS Cognito
NoPass.me - Open-source identity verification
Velix.ID - Frictionless Identity verification through Blockchain
TypingDNA Authenticator - 2FA codes in your browser, secured by the way you type