Just google topaz and click on the first link :P It's actually designed as a photography program but somewhere down the line gfx artists started using it for tags...most common filters used are clean and adjust. You can download a free trial version on their website
It's also one of the most controversial things among the gfx community because half the people see it as the devil and half think its awesome
I'm in between btw :P It works well at cleaning and sharpening your tags, but if you overdo it, you lose a lot of depth and detail.