The company is called Slab (somewhat of a double reference to a thing you can write on and slab serif fonts). It is current in private beta but if you would like to take an early look please find my email in my profile and I would be happy to share with HN.
We is much simpler and easy to use and plays well with the non-Atlasssian ecosystem (as well as with JIRA). In both these regards we like to think of ourselves to Confluence as Slack is to Hipchat.