Slack
Slack is a popular chatroom service that Free Code Camp outgrew
As much as we enjoyed using this service, it is a poor fit for large open source communities. This said, many open source communities still use Slack, and Slack does nothing to discourage this practice.
If you're curious, you can read about Slack's false advertising and the debacle this caused in June 2015.
Free Code Camp now uses Gitter.