I have just installed Automatic Thread Tagger.
When a member submits a new thread this modification will automatically take keywords from the thread title and use these as tags. You can use Automatic Thread Tagger to propose the member AJAX tags for his new thread, or it assigns new tags after saving the new thread. It can add the translated thread prefix to the tags.
As an example, if a member submits a thread with a title of "Fish Food for Cats!"
The thread will be automatically tagged with:
If the member also submits an actual tag of "Fish", this will not be duplicated.