Files-11 is a file system used in the RSX-11 and OpenVMS (which, despite its name, is closed-source) operating systems for DEC computers. It takes after some other DEC file systems, such as that of TOPS-20, but is more sophisticated.
Files-11 supports a hierarchical directory structure, using a syntax very different from the better-known Unix style using slashes (or the DOS/Windows one using backslashes). Dots, colons, and square brackets are all part of the means of expressing the devices, accounts, and subdirectories leading to a file. File versioning is also supported with a colon followed by a number at the end of the name.