The "Forum Addon" - is a tool that allows the creation of multi-topic/thread based forums for discussion and collaboration.
The stream based interface of a "group channel" is a good tool for slow moving conversations, but things easily get "buried" once they move off of the first page or two so that in a larger group, it becomes easy to miss important threads.
The "Forum Addon" addresses this and a number of other issues by creating a more traditional topical interface with each thread assigned to a given topic. Forum members with appropriate permissions can post to topics either from forum page of the hosting channel or by sending a DIRECT MESSAGE to the hosting channel and including the appropriate hashtag.
The Forum Addon extends the standard Hubzilla permission controls by allowing the channel owner to set independent permissions for reading and posting on a per-topic basis. Forum visitors who attempt to remotely post to a topic for which they don't have permission receive an error message indicating their lack of permission. Visitors who use the forum posting interface but do not have permission to post will not be presented that topic in the Topic dropdown.
Channel owners can allow visitors to self-subscribe to topics as "readers" of the topic, or they can enforce a manual subscription model. Self-subscription presents a "Subscribe/Unsubscribe" in the heading of each forum topic. Manual subscription would allow integration with the HZServices submodule of the CART plugin to allow the creation of forum topics with paid subscriptions. Of course, it is also possible to manually subscribe a user to a given topic.
Per topic permissions use privacy groups to assign permission to read or post.
Version 2.0 is nearing completion and will be the first public release of the "Forum Addon." It is expected to be released by March 15. You can see the Forum Addon in action at the DM42 Hubzilla Addons forum.