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.
privacyIDEA is a modular authentication server that can be used to enhance the security of your existing applications like local login, VPN, remote access, SSH connections, access to web sites or web portals with two factor authentication.
The WiKID Strong Authentication System is a highly scalable, secure, self-hosted two-factor authentication system. It is simple to implement and maintain, allows users to be validated automatically, requires no hardware tokens, has a simple API for application support (via Ruby...