A base coat, that is supposed to fill up ridges.
I got it as a present when I bought another ESSIE base coat and I must admit I was very happy didn't pay a cent for that.
The application was easy. I dries up is seconds and leaves a matte finish.
I can not say if it fills the ridges or not, because I don't really have any. The surface of the nail felt very smooth, though.
The biggest problem was, that I couldn't apply my nail polish on top of it. I did wait until it was 100% dry, but still - the brush with the nail polish just couldn't glide on the nail and got "stuck" (hope you understand what I mean). I had to take it off and start all over again, with a proper base.
If you want to use it on its own for a matte look - Great. But as a nail polish base - BIG NO NO!