SK files store graphical user interface themes (so called ‘skins’) for rhythm game Osu! available for Microsoft Windows. OSK should be saved in ‘Skins’ folder, located in game’s installation folder.

Osu! is a computer game that tests users reflexes and sense of rhythm. OSK skin files can be used for modify visual aspects of the game. Fan-created skins can be downloaded from internet forums dedicated to Osu! game.