IRC
Find us on Freenode, channel #lemonldap-ng
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Mattermost
Free Slack service hosted by Framasoft: https://framateam.org/lemonldapng/
We use OW2 JIRA to list bugs and features. You can first check on LemonLDAP::NG JIRA project that your bug is not already referenced, and then create it (with a registered account).