Lobster

From Free Gamma:

Lobster is not a plugin but a Photoshop droplet that creates four new layers from your file: Luminosity ( a very specific type of tonality) and Red, Green & Blue Chromaticity (Hue and Saturation). These separate layers offer you unprecedented control and power over your RGB files.

Lobster makes many dialogue boxes, tools and histograms more accurate. If you have not previously understood the feedback that you were getting from Levels and Curves - with Lobster you will understand why - and now these most essential dialogue boxes will become ACCURATE and MUCH more powerful. If Dodging and Burning changed your colours as well as your tone - this will now cease. If Sharpening created unpleasant digital artefacts these will be reduced.

If you are an artist or photographer, Lobster provides accuracy, control and new tools for creativity.
If you are a curator, an archivist, or are working in medical/scientific image preparation and analysis, Lobster will become an essential part of your toolkit to ensure accuracy and avoid misleading changes to digital images.