File with an .OSZ extension contains a save of the osu! game – music, graphic, location and time in which clicks are to be performer according to played rhythmic map, all in form of a singular ZIP compressed file. Such packages can be opened both with the osu! program or some simple program supporting ZIP compression.

OSZ files enable to save and co-share untypical gameplays within the game, which consists of rhythmic clicking on images, according to music. They enable users creating unique so-called beatmaps. If the osu! application is installed in Windows, files can be opened by double-clicking or dragging them onto game’s window.