PXMBoard (PHP XML/XSLT MySQL) is a php based forum software. It supports smarty and/or xslt as template languages and mysql or postgresql as dbms.
The PXMBoard software features a different approach to a bulletin board. Rather than to line every post the way down, spreaded over several pages, it offers a real thread view. The layout has usually three frames, aligned from top to bottom. The top frame contains the topics, the middle frame the thread with the answers and the bottom frame the message body, e.g. the text of the post. With PXMBoard, you always know who answered who, without the need to quote names. This forum system also is very fast and a joy to use, once you get the hang of it.