Alerts you about some basic events in game.
Works even if you've disabled sound effects.
Works alt-tabbed if you have "Sound Background" option checked in WoW.
Queuing to LFG
LFD/LFR queue ready
Battleground queue ready
TB/WSG queue ready
Inactive debuff (untested)
There are many addons that do the same, but I just wanted a very simple one.
I hope someone finds this useful.