The following plugins have been suggested:
- StatusNet
- Mahara
- Launchpad
- Drupal
- Django
- Moodle
- Wikkid
- Thunderbird - aging, last update quite a while ago
- Thunderbird or GitLab repo
- pfaces
- GMail
- GroupServer/OnlineGroups.net
- gnus
- Redmine - Feature #9112
- Pidgin
- BuddyCloud
- Gitlab
Feel free to talk to us if you have any questions.