ThreatMeter by D4KiR for WoW Forever

What it does

• Shows a threat window styled like the game's Damage Meter, with one bar per player of your group or raid against the enemy you target
• Lets you pick what the bars show: the threat value, the percentage of the tank's threat, the percentage needed to pull, or the value together with one of them
• Can add pets, a pull aggro bar and the highest threat of other players it can see, such as nameplates and mouseover targets
• Has an optional Classic Threat Display, the older style that puts your highest threat percentage as text near the middle of the screen
• The window can be moved with the game's Edit Mode, resized, locked, collapsed and reset from a small menu, and the background opacity is adjustable
• Comes with a minimap button and settings in German, English, Spanish, French, Italian, Korean, Portuguese, Russian and Chinese

In WoW Forever

Yes, ThreatMeter by D4KiR has a WoW Forever version (version v0.7.4-forever of October 14).

What the addon rules allow

For the same job

• Details! Damage MeterForever buildThe standard damage and healing meter of Retail and Classic.
• ThreatClassic2Forever buildThreat meter for party and raid members against your target, with pull aggro bars and warnings.
• Skada Damage MeterNot updatedLightweight damage meter used as the small alternative to Details.
• Forever Details MeterForever buildLightweight damage, healing, absorb and threat meter that reads Blizzard's C_DamageMeter and UnitDetailedThreatSituation.
• Recount - RevivedForever buildMaintained revival of the graphical Recount damage meter.
• ForeverThreatForever buildOmen-style threat meter built for Forever.

Every addon: Damage and threat meters