An interface defines a lot about what you are working on. And the same an awesome graphic user interface defines a lot about the graphic interface you are having on board. In this article, we have collected awesome (but yes free) GUI sets for you which you definitely wish to use for your future projects.
Polaris UI
Image Source: DesignModo
Balio
Image Source: Webdesigner Depot
Pillow
Image Source: Dribbble
Square
Image Source: DesignModo
Dashboard
Image Source: GraphicsFuel
Apollo
Image Source: DesignShock
Hades
Image Source: DesignShock
LinkedIn iPad
Image Source: Zeki Ghulam
Sign In Form
Image Source: Mahdi Pourebadi
Metrostyle
Image Source: Josep Roselló
Web App UI
Image Source: Blaz Robar
Google+ UI Kit
Image Source: Alexey