Using this service, you can create your own web discussion forum or "assembly". This offers you a discussion forum in single-page threaded format. New assemblies are automatically categorized into the Assembly directory.
Bravenet offers a package of free webmaster tools, including discussion forums. The forums use the popular cascading threaded format to display threads. Various aspects of the forum's presentation can be customized, such as the title graphic, title, subtitle and colours. Note that a free membership to Bravenet gets you access to all the tools, not just the discussion forums. Bravenet offers a premium service level if you want to eliminate ads from its remotely hosted tools.
One of the server.com family of free online applications, DiscussionApp enables you to set up a discussion forum that will support up to 2,000 posts. You can customize the look of the forum in various ways, and there is an integrated mailing list facility that allows people to subscribe to a daily update of new posts.
Remotely hosted bulletin board service, which allows you to create unlimited discussion forums. Each forum you set up can have its own look and feel, and you can specify moderators for each one. Both end-users and administrators have a wealth of options at their disposal. For a small monthly fee, EZBoard users can remove all advertising from their bulletin boards.
If you're looking to hold a limited-duration discussion or a discussion with a small number of participants, Quick Topic offers one of the simplest and most frictionless solutions around. Essentially the equivalent of a single "thread" in a regular discussion forum, a Quick Topic forum offers an environment where discussion participants can just turn up and post. There's no registration required - security of sorts is assured by allocating an extremely long random URL to each Quick Topic forum so that the URL is essentially unguessable. All you need to do to get the discussion flowing is fill in a quick form and mail the URL of your discussion to the people you would like to invite to it.