matterbridge
bridge between mattermost, IRC, gitter, xmpp, slack, discord
...The project supports bridges between services such as Discord, Slack, Telegram, IRC, Matrix, Mattermost, Microsoft Teams, Rocket.Chat, Twitch, WhatsApp, XMPP, Zulip, and more. It can handle multiple gateways, message edits and deletes, attachments, private groups, and threading when the target platform allows it. Mattermost is not required, despite the project name. matterbridge is useful for communities, open-source teams, and organizations that need cross-platform chat continuity without forcing everyone into one service.