File Operation Window
File Operation Window is a free UI design resource made by Dribbble user Fery Wardiyanto. As far as I can tell, its license is Creative Commons Attribution-NonCommercial-ShareAlike.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.