Is it possibe to write a plugin to make wordpress act like a forum - the last commented post goes to the top? How this can be achieved?
You can actually make Wordpress look & behave similarly to Stackoverflow with this: http://p2theme.com/ (demo here: http://p2demo.wordpress.com/). I'm sure that it is configurable to put recently commented posts/threads to the top.
firt use this function to get comments
http://codex.wordpress.org/Function_Reference/get_comments
in $args pay attention for order and orderby
then you will have array and in one field you will have comment_post_ID. this is id of post, so having this, you can query for post content