privacyidea
two factor authentication management system
...Its modular design makes it easily enhancable. It runs on Linux.
Applications and workflows can be connected to privacyIDEA hence enabling two factor authentication in your system logon, web applications, SSL VPNs, firewalls and many more.
A detailed audit log gives you full control of what happens when, where (why? ;-) and by whom.
A demo site is available at demo.privacyidea.org.