TargetWatcher

This is a simple addon that allows you to select a member of your party or raid. When you click the frame, it will automatically target that unit’s target (Target of Target). If you are playing a class with a pet and are not in a party, the addon will automatically select your pet when it is active.

The addon also includes a small built-in color indicator that monitors your threat level compared to  selected unit. If the threat becomes too high, the indicator will flash to alert you.