This offering is expected to become legacy soon. We plan on moving to a different platform soon. When that happens, Mattermnost will move to lifesupport-only support with eventual removal of the platform. However, no concrete plans are in place right now.
See https://lab.libre.moe/limo/limo/-/work_items/58 for current information.
We use Mattermost as our chat system. It works similar to Slack or by extension Discord and allows us to have channels for topic-based community chats. Users can also create new channels or different Teams, which are analogous to Discord's Servers.
The above link will automatically join our common team (read server) when you login, if you wish to not do so, click this link: https://chat.libre.moe
Mattermost doesn't allow SSO in the open-source version of the software. This was previously available, but was removed since version 11. You will need to create an account local to the Mattermost server.