That's all good, but the differentiating factor of Slack over Hipchat & the like is how well it integrates with everything your team is likely to use. It works seamlessly with Github, Trello and IRC.

I don't mean to devalue this product at all, but This is not a viable Slack alternative, it's a generic (and good looking) communication tool. This said, I commend the open source approach, it could probably help the product evolve towards something much better and integrated.