Threatening shows a simple threat meter next to the target frame. It displays your threat on the target as well as your pet's threat on the target.
Because Threatening uses the brand-new built-in threat API introduced in Wrath of the Lich King, it does not update very often (or at all) when you or your pet's threat is below ~70%. This is not a bug in the addon; that's the way the client reports threat.
New in v0.03
Fixed for Beta build 8788
New in v0.02
Shows party members' threat
Has colored bars
Does not show threat for dead units
Has movable bars
v0.03: Fixed for beta build 8788
v0.02: Shows party and party pet threat, has colored bars, does not show threat for dead units, has movable bars