This is one of over 4599 effects generated by Filter Forge, a Photoshop plugin that allows you to create your own filters.
To open this filter, you must have Filter Forge 2.0 or higher installed on your computer. If you don't have it installed yet, click here to download Filter Forge
On its own, serves much the same function as switching to indexed color with a specified color table, but it's really better suited as a pre-processing step dropped in to other filters... works great with artistic filters, for example, specifying which colors of crayons you can use in a crayon filter.
limited indexed color table palette