I have tried several quite famous forum systems. I found most of them are category-centered style. If user wants to post a topic, first he has to find a category. I wonder if there're some forum systems which are user-centered. That is to say, all topics are structured surround the users. User can post a topic, then he can 'tag' with some categories. I found Flickr do in this way and wonder if there're some such forums.
I'll be very appreciated that someone can give me some hints. Thanks
Interesting question, nomatter. All of the forums I'm familiar with are topic-oriented. Flickr's approach using tagging is relatively new. I haven't seen a program to duplicate it, but you might try searching script archives for "flickr" and see what turns up. Or, the main SEs for "flickr clone".