u2f

Protect your applications with Single Sign-On and 2 Factor.Authelia is an open-source full-featured authentication server available on Github.

Okta's Workforce and Customer Identity Clouds enable secure access, authentication, and automation—putting identity at the heart of business security and growth.

OnlyKey is an open source alternative to YubiKey. OnlyKey natively supports: a hardware password manager, multiple two-factor methods (FIDO2, TOTP, and Yubico® OTP), passwordless SSH login, and OpenPGP.

Solo is an open source security key, and you can get one at solokeys.com.