I've been thinking about writing my own forum code (in PHP, unfortunately, because tmy $4.95-per-month webhost provides a MySQL account and PHP scripting support). I really have no idea what subject the forum would take; it'd probably be an adjunct to the blog feature. Basically, I'm planning (but too lazy to get much code down) a forum+blog+address book+MUD (maybe). Ideally, I'd like to have it highly extensible, but PHP isn't exactly the most object-oriented language around.