Duo SSH - Duo can be easily added to any Unix system to protect remote (SSH) or local logins with the addition of a simple pam_duo PAM module. It has been tested on Linux, BSD, Solaris, and AIX. The code is open-source and available on GitHub. Look at the walk through video to protect a Unix system with Pam Duo| Cisco Duo
Add two-factor authentication (2FA) to 1Password with Duo Single Sign-On.| Cisco Duo