The Last Activity screen allows you to see which work product entries were last worked before a given number of days ago.  You can also search for entries that last worked on in a days range.

The last day worked on is obtained from the date and time of each History entry made.

You can also see the last date a specific associate worked on which work product entry by selecting the associate name and clicking on the By Assoc? check box:

As this example shows, the cases that CF worked on, and the last activity by the associate are shown.