Wikipedia
LinOTP
LinOTP is a Linux-based solution to manage authentication devices for two-factor authentication with one time passwords. It is implemented as a web service based on the python framework Pylons. Thus it requires a web server to run in.
LinOTP is mainly developed by the German company LSE Leading Security Experts GmbH. Its core components are licensed under the Affero General Public License.
It is an open source authentication server certified by the OATH initiative for open authentication for its 2.4 version.