This is a very minimalistic HUD. You get a health and resource bar for yourself, your pet, your target and focus, and their targets. Druids also get a mana bar in cat or bear form, and death knights get rune cooldown bars. You can also create your own custom bars, to track most anything.
Cataclysm features have also been implemented. Balance druids get an eclipse bar, warlocks get a soul shard bar and paladins get a bar for holy power. These features will not be present on live currently, but will automatically become enabled once 4.0 is released - no update will be needed at that point.
To customise the size of the bars, use the command /tutti hud options. This brings up the options frame, where you can change these, as well as the threshold for when the health or mana bar turns red, and the frames' update rate, if you should need it.
To create a custom bar, use /tutti hud custom. Colour, size and orientation (vertical/horizontal) define the looks of the bar. Value and max functions are Lua functions, and need to return a value (examples below). The name is not very important, but is needed to remove (delete) a bar.
Examples of bars:
_,_,_,s=GetSkillLineInfo(13); return s
_,_,_,_,_,_,t=GetSkillLineInfo(13); return t
This will give you a bar that tracks the 13th item in your skill window, most likely a weapon skill. For my druid it was staff skill.
_,_,t=UnitDetailedThreatSituation("player","target");return t or 1
This will give you a primitive threat bar that shows you how close you are to pulling aggro off whoever has it.
Note that custom bars can easily cause Lua errors. If you need a bar that can't "run" constantly, you have to make sure it doesn't.
2.0: Bars will now follow the UI scale, and will hide along with everything else when you hide your UI. Default values have been increased by approximately 40% to compensate, though this will not affect any saved settings.
2.0: Custom bars will work as intended now.
2.0: Pet health and resource bars have been added below your own.
2.0: tuttiHUD is now Cataclysm ready. With version 2.0, once Cataclysm is released the additional bars will appear automatically, no update needed.