My girlfriend make cross-stitch. She started to design her own pattern. The problem is that it's not always easy to find the right color for the thread from the hundreds of available colors. She then asked me to make a script that will find the closet DMC color from RGB values. And that's what I did. It took me an evening to make it work! It's a very simple PHP script with some JavaScript for the form.

You can try it on her web site : Elaida.org

Also look at her awesome retro-gaming key rings that she made with the help of this script.  ;-)