The last activity page would show the latest X members like the other pages, only 1 entry on the page per member, and where they stopped in the forum.
"Popowich was last seen viewing..."
"AndyB was last seen viewing..."
"MemberX was last seen viewing..."
Fill in the white space with the date to help see today vs yesterday etc i suppose is useful.
The information already exists in the db. It can be seen when clicking a member profile.
For me, I'm interested in where new members stop, for example last thread viewed, so I have the option to start a private conversation with them asking if they need help.
That gets into optional run time filters such as only show me members with 0 posts on the page.
Is this only useful to me? Anyone else that would find this useful?