Do we have a rankings system for xenforo like this:- http://entrance-exam.net/forum/rankings.php , where members earn points per reply and are ranked as per their points during the cycle of 15 days/month or set by admin ???
or if it isn't available , suggest me some developers who can custom develop this for me/us.
XenForo has a trophy system which does exactly that... it awards points based on criteria that you set (which can include post count). The points aren't used directly for any kind of rank or badge system. There are addons available: