What nkRebuff does is very simple: It tracks important buffs, cooldowns and debuffs and tells you what you are missing. So in difference to a buff bar addon which shows you how long a buff is still active, this addon will tell you exactly when to renew an important buff on you or debuff your target or when an important ability is ready again.
In the configuration you can tailor the list of things to be watched exactly to your needs. You can even change the default behaviour and show things as long as they are active.
nkRebuff has been heavily tuned to deliver the best performance possible. In almost every situation it will not even show up in the ingame addon performance tab. If you care about performance then nkRebuff is definitely the best choice to monitor buffs, debuffs and cooldowns.
There is a extensive ingame documentation of the addon available. Simply click on the option 'manual' in the nkRebuff menu you can access through the nkButton at the minimap.
Please report bug or feature request either through the tools available on this site or by sending me an email at firstname.lastname@example.org.