bridge between mattermost, IRC, gitter, xmpp, slack, discord, telegram, rocketchat, twitch, ssh-chat, zulip, whatsapp, keybase, matrix, microsoft teams, nextcloud, mumble, vk and more with REST API (mattermost not required!)
Why do you think that https://github.com/libremonde-org/paper-research-privacy-matrix.org is a good alternative to matterbridge