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 :)
For me, primarily the performance tbh. Chatto just flies and Slack feels incredibly sluggish. And from the "vibes" it just feels better designed, I like the overall user experience, it feels technologically solid but also looks nice and works how I feel it should. Hard to put my finger on it exactly.
In terms of inspiration and also the market that I want to go after with Chatto Cloud, this is definitely aiming to be an alternative to Slack, Teams, Mattermost et al. I've tried to make it friendly and casual enough to _also_ work as a Discord alternative, though.
I've been trying to find a Slack replacement since Salesfarce started ruining it and I must have tried out maybe 50 potential replacements, paid and free. This is the first self-hostable, open source one I've seen that doesn't look like design is the very last item on an amorphous future roadmap. In fact, there's some really nice design and UX touches in Chatto. Congrats on the launch, I'm absolutely certain we'll move off Slack to this when the dedicated apps arrive, maybe even before.
I also maintain a Chatto bot framework and a Tauri client, need to update those now :)