Originally posted here by tampabay420
www.phpBB.com (BBS, community style- i think that's what AO is?)
http://phpnuke.org/ (news server, would work with silly content )

there are tons more, just use google

btw- this is of course if you're going to use PHP (i suggest it)...
Just for the record, AntiOnline runs on vBulletin, not phpBB.