vBulletin and FUDForum have very similar functionality and are both implemented as PHP. They appear to both be very similar:
- http://www.forummatrix.org/compare/FUDforum+vBulletin
- http://www.forum-software.org/forum-comparator/fudforum-vs-vbulletin4
(The later compares an old version of FUDForum). The main differences are outlined below. More detailed comparison would require trying them both.
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