Q&A discussion threads
Discussion forums allow discussion threads (called topics) be be created. Visitors can engage on specific discussions on specific topics.
I understand the recommended discussion tool is the Q&A facility. If so, users should be allowed to create and contribute to specific topics as well. The list of active discussion topics could be shown on the Q&A main page allowing the user to pick a topic. Some customization would be good to have, so that users can show/hide discussion topics they are interested in or not.