Forum Moderators: rogerd
If you're looking for something sitewide, you just have to make a simple script to count how many different IPs have viewed any page on the site within, oh, say five minutes, if you figure that's how long it takes to read the content on a page. That's pretty much what the scripts inside BBS packages do.
Depending on how long a threshold you allow, this might artificially inflate the actual # of people you have listed as being "actively" on site. But hey, This is the net. Creative statistics are what keep people like epinions going ;)