I've been looking for a chat application similar to the original slack (prettified / integrated irc, no need for the various integration and all) but free and s

I've been looking for a chat application similar to the original slack (prettified / integrated irc, no need for the various integration and all) but free and self hosted or for a fixed sum rather than a sum per user per month, but I have been disappointed in what I found. The self hosted version of tools that offer a subscription service like mattermost are very limited in search and archiving, the ones integrated in hardware appliance like synology chat are very limited in admistration capabilities (moderation, permissions,...). Did I miss an offering somewhere or is this a still open area? Main needs 1-1 chats, channels, permission per user per channel, full logs and search, administrative view and archiving over all exchange