This is Painter's Wheel - a very powerful color picker and mixer for Adobe Photoshop CS6. And older version for CS5 is available as well.
Painter's Wheel is a very powerful color picker and mixer containing a Hue-circle and a HSL-triangle. Painter's Wheel also allows the user to create a gradient of several color swatches between the foreground and background color. The user can then increase this gradient at will. This allows for example, a very quick way of finding average colors between the FG and BG - but it has many other uses as well.
All credit goes to Len White for developing this plugin. I DID NOT develop Painter's Wheel so don't bother asking me about help if something is not working.
I have the full permission of Len White (firstname.lastname@example.org) to redistribute this Photoshop plugin as long as full credits are given to him. It is a free plugin but donations are welcome at lenwhite.com
Older version (CS5):
An older version can be found here: Nerdchallenge.com