Piazza is the state of the art for online classroom discussions. My students and I experimented with numerous leading systems over several weeks. Piazza won hands-down. In fact, my students preferred it so much we ended the comparative experiment early, on humanitarian grounds.
We're all enjoying using Piazza, and from what I understand, both the students and the instructors are finding it useful. It does seem like putting all the students together ensures a faster response time for most questions.
I love using Piazza for answering student questions; the user interface is unbelievably nicer than anything else I've seen. It is easy to enter text and easy to see what questions need answering; It is just easy to use.
Instructors can create a Piazza for their class with a single click.
Students and instructors are automatically enrolled with appropriate roles, based on the course roster.
When clicking on Piazza in CourseWorks, users are automatically signed in to Piazza, so there's no need to remember a separate user name and password.