You are integrating privacyIDEA into your application? You want to use an existing authentication plugin like the plugins for ownCloud, for OTRS/KIX, for PAM, RADIUS or whatever?
Or you want to write your own plugin to add 2FA against privacyIDEA to your application? Then this category is the right choice.
You may also read: http://privacyidea.readthedocs.io/en/latest/application_plugins/index.html