Comment by mdaniel

Zulip is also, last I checked, the only ones who offer completely free, archive-enabled, hosted chat for open source projects ( https://zulip.com/for/open-source/ ). Mattermost has some kind of "out of the kindness of our heart" setup, but it requires applying for it ( https://docs.mattermost.com/about/license-and-subscription.h... ), and Slack appears to actually retain the archive content, but only makes it available for those who pay