Why do we need a list of active members? If you see a recent post by someone, you know they're active. If you want to see if a specific person is active, look at their profile. All the active members know who all the active members are, and it's the new members' (you) jobs to find out by posting or lurking.
We have a
members list just like the one you linked to. It can be ranked by name, join date, number of posts and last post. So maybe that's what you meant.