XUGJ (XOOPS User Group Japan) has exchanged Q&A Forum with d3forum. Excellent!
Old Q&A forum had used plzXoo which is like "Yahoo Answers". But, excellent forum is good for Q&A. For example, MSDN and other technical forums doesn't use "Yahoo Answers".
D3Forum has review feature. That's really useful and my favorite, because it is like MSDN "Was this post helpful ?".