A quote from their website :

"Infinity Textures (short I-Tex) is a powerful, image based Texture Designer and Generator. It was never so easy to get stunning beautiful seamless textures. I-Tex gives you the ability just to draw your texture on a tiled surface using ClipDraw-Technology and the collection of more than 130 high flexible texture modification functions."

I think it's one of the best texture programs around and I like it a lot!