The addon in question was an audio addon.

It Spoke out loud when your cool-downs were off. Example: If you were a priest it would say "Devouring Plague Ready!"
It used a TTS voice very similar to GladiatorlosSA and Sound Alerter, however it is NOT those add-ons. I think it used a collection of .wav/.ogg files.

I can't recall the name of it.

Just to reiterate. It didn't announce the cool-downs of OTHER players only MY cool-downs.