Killium is an addon that assists with priority queues and rotations for maximizing DPS, by providing a custom action bar/target window and highlighting what to click next based on configured rules.  Killium will "compile" all of your rules into a single configuration string, making sharing configurations as simple as copying and pasting a single line of text.

Killium has a very configurable priority based rule editor with the ability to specify what buffs or debuffs have to exist on either you or the target, as well as as how many stacks need to exist to trigger the rule.

Blizzard is making DPSing and encounters in general more complex.  Many DPS specs now have to be aware of how many stack of buffs/debuffs exist at an instant in time or they will DPS sub-optimally.  This addon can assist by allowing you to concentrate more on one area of the screen.   It will not assist with staying out of fires, but it will help allieveite a mage from having to be as concerned about if you have enough different dots on a target before you waste a combustion with little or no effect.   It will help your mage to know when to re-cast living bomb without having to look on the other end of the screen if you already have living bomb up or not.  It will help your shadow priest decide if it should cast Mind Blast or Mind Flay at that instant in time.

This addon does not do any theory-crafting or make any decisions on it's own.  It requires rules to function.  It is assumed you or someone else has already done the theory-crafting and have made a rule set based on that theory-crafting.  Killium makes it's suggestions expressly based on the rules that have been input to it.