Note that rocket chat can federate [1] over matrix [2], and I believe mattermost can as well. [1] https://matrix.org/docs/projects/as/rocket-chat-federation.ht

Note that rocket chat can federate [1] over matrix [2], and I believe mattermost can as well. [1] https://matrix.org/docs/projects/as/rocket-chat-federation.html https://matrix.org/docs/projects/as/rocket-chat-federation.h... [2] https://matrix.org https://matrix.org