Slack
From Dreamwidth Notes
Staff, contractors, and some developers, support volunteers, and affiliated conference attendees, can use a Slack team to communicate in real time from a variety of devices.
In practice, there is a flurry of logistical communication around any given official conference, and intermittent purpose-focused chat on other topics (such as particular development issues or downtimes).
If you need to be invited to the team, check in with a staff member or senior volunteer.
For general development and social chat, see IRC.