Talkyard is new (year 2018) open source Q&A software, inspired by StackOverflow, and forum software like Discourse.
In addition to Q&A topics and categories, you can have open-ended discussions, and Slack like chat channels. So people can go to your place, not just for Q&A, but also for talking and being social. You can have private staff categories & chat.
Here's an example discussion — copied from StackExchange/StackOverflow: (cc-by-sa license)
Talkyard is beta software currently (May 2018) and I'm developing it. GitHub repo here, and SaaS hosting here. Screenshot:
(The posts are from this StackExchange question, license: cc-by-sa-3.0)