MSAccess2000 or SQL Server based Forum. Totally Free.
Features:

* Fast Easy to setup and scalable
* Database-backed with Access or MS SQL Server
* Unlimited forums, posts, and members
* WYSIWYG RTE Post Editor
* Easy to modify commented code
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World's first user-skinnable message board! Web-Based Administration, WYSIWYG Editor, Emoticons, Bad Word filter, Integrate w/existing member db, API, Email notify, Language files, per-forum security, moderators, SQL Server/MSAccess and PROMPT EMAIL SUPPORT!

Snitz Forums 2000, one of the best ASP based bulletin board systems on the market. Getting better every day! A complete board system (forum) that allows the user access to a friendly and intuitive interface.
Features:

This is Version 1.00 of an ASP Forum including a CMS Administrator. Modify the db configuration to make it functional in your environment. [(:-)]

MegaBBS combines the powerful features of PHP boards, along with the ease of programmability and installation of ASP! Although MegaBBS has only been publicly released since late June 2002, it has already gained a great following of other users and developers. Current uses of MegaBBS include corporate intranets, commercial websites, personal use, and universities! It supports MS-Access and SQL Server and can be setup and running in a matter of minutes.

JGBBS is a tree-structured online forum system designed for small to medium sized communities, we manage to keep it neat and simple, yet integrated with many useful features.

iyzi Forum started as a project to provide my friends a small discussion place and has been continued for 3 years. Although the philosophy behind it is to keep simple, it includes a lot of features to meet people's needs. I also tried to keep it as secure as possible.

fipsForum is a simple and easy to use Forum System with a MS Access database.

ASP-DEv Forums are back, full XML output (HTML for non-compliant browsers), fully skinable using XSLT and CSS style sheets, avatars, group based permissions, private messages, attach files to posts, multilingual, moderated forums, each forum has its own permissions for Read/New Topic/Reply, encrypted password, Secure cookies (no username or password contained in cookies), who's online, sticky/locked topics, supports clustered web servers plus much more. UPDATED: Forum now supports subforums, IP Blocking, Uploadable Avatars, database caching and more