SimpleUnitFrames is an extension to the default WoW Unit Frames. Rather than a complete unitframe replacement, this addon adds further information and features to the existing frames and allows a greater degree of customization to enhance their usability.
The v2.x.x series of SimpleUnitFrames involved a complete re-write of the code, however credits go to Rophy and xan for their original work on the v1.x.x series.
All configuration for SimpleUnitFrames can be performed through the Interface Options panel which can be opened through the slash commands /simpleunitframes or /suf.
For more info on SimpleUnitFrames, check out the Project Page.
Comments, suggestions and feedback are welcome here, but if you have bug reports please Create A Ticket.
I wonder if you would consider adding buff/debuff functionality to SimpleUnitFrames? What I mean is by default the Blizzard Unit Frames don't show pet/party buffs unless mousing over them which is very annoying, also by default the target frame doesn't show the full amount of debuffs.
There is only one other mod that does this but it's currently non functional in 3.1 and the author doesn't have much time for coding mods these days.