ThreatBar

Minimalistic threat addon showing your threat (big bar) compared to the current tank (left bar), showing percentage and absolute difference, and visualizing when you will get aggro (taking into account if you are ranged or melee). When instead you are tanking, the secondary bar will show the player second to you on threat.

The bar only shows when you are in combat. Alt-drag to move it or Shift-drag to resize it.