Unary Filesystem is a unique OS, as it has no concept of files, only folders. Each folder is nameless and can contain either one folder or no folder. When the OS is first booted, there is one folder, which can't be deleted. Deleting a folder results in all its "children folders" being deleted as well. Each folder has no folder by default, but the user can create one.
The Unary Filesystem OS can be run as a program. When this happens, its deepest folder (folder F) is located, and its depth (including the topmost folder and F, depth is 1 if it is the topmost folder) is interpreted as a Unary program.
Since Unary is Turing-complete, Unary Filesystem is also Turing-complete.
Code golfing potential
Unary Filesystem can technically solve any problem in 0 bytes, making it the ultimate golfing language.