I've been testing/using chatto since early on and I'd say it's both and neither. It feels much nicer to use than Slack, but as of now it's missing some of the more "Enterprise" features. I would probably say it's a Slack-like Discord? But from the architecture it would be capable of playing as a full Slack replacement.

I also maintain a Chatto bot framework and a Tauri client, need to update those now :)

What makes it nicer to use than Slack?