Palette Creator with Matching Colors
Here you can generate a 256 colors palette based on a "pivot" color. It's done by ranging a suitable value concerning your input color like a RGB channel, saturation or brightness.
Usually from the result palette you can choose nice colors to combine with your pivot color. It can be used to find colors to make gradients, "tone over tone" combinations, etc.
It's very usefull, for example, to help deciding what colors to use together in software interfaces.