This one is an online dice roller that is intuitive, attractive, and effective.
The example above called for one Proficiency die (yellow), two Ability dice (green), one Challenge die (red), and two Difficulty dice (purple). Note that the unselected dice are shaded. When you click on a die to select it, it appears clearly or highlighted. The string of symbols along the bottom are the calculated results minus the symbols that cancel each other out. A nice feature is if you hover the cursor over any of the images, a box with a label appears.
Another cool feature is the ability to view the probability of the result.
A very solid gaming tool for the Star Wars RPG. I'll be using it and look forward to seeing more like it.