Unanswer threads
 

In the drop down menu next to the search button is a list of options. One of them is Unanswered threads.
Is that option a mod for 3.8 and is it available to download?

I tried several search key words but nothing showed up.

Its simply a shortcut that runs this ;

....../search.php?do=process&replyless=1&replylimit=0&exc lude=30&nocache=1

You probably dont want the exclude bit, that just excludes the paid requests forum here.