Date Field Lookup is an ACT! Add-On which lists all your contact database date fields and allows to do lookups based on the date value of any of these fields.
Of course, it is already possible to lookup date fields in ACT!, through a lookup by example, for instance. But you can't do any relative lookups, for instance:
Date > Today - 30 days
Below is Date Field Lookup's main screen. It is self explanatory.