We paid for screenhero before they stopped charging. Last I heard, it was not as good as it once was now that it is part of slack. That aside, my work looked at going to slack and it was shot down vs staying with hipchat for a few reasons. Partly the cost of slack itself and partly the cost of chat bot rework (we have an unhealthy coupling of chat bots to hipchat that make it hard to migrate them to slack apparently). The bot(s) handle pr workflows, build jobs, internal service disruption comms, paging, and more.
GitHub issues for taggable discussions.
Zoom.us for calls and beer hangouts.
Google Docs for collaborative writing.
Screenhero for pairing/reviewing together.