FlatForum is a fast, clean, and simple threaded forum that uses a flatfile database. It's designed for people who have small to medium-sized websites and don't want a huge, bloated forum like phpBB.

Features of FlatForum:
- Small and fast. The required files for FlatForum are less than 150k combined.
- Uses an optimized flatfile database. Unlike most flatfile forums, FlatForum won't bog down when your forum starts to get a lot of posts, because it doesn't load the entire database for each page view.
- Easy to customize. You don't have to muck through the forum script to change the appearance.
- Autolinking that WORKS (all URLs and email addresses).
- Identical appearance in IE, Mozilla, Firefox, Opera, and Netscape.
- Optional word filters (censors).
- Advanced spambot protection without requiring user registration or captchas.
- Free :)