Pseudo- and virtual file systems

• devfs – Virtual file system in Unix-like operating systems for managing devices on-the-fly
• debugfs –Virtual file system in Linux for accessing and controlling kernel debugging.
• procfs – Pseudo-file system, used to access kernel information about processes
• tmpfs – in-memory temporary file system (on Linux platforms).
• specfs – Special File System for device files
• sysfs – Virtual file system in Unix-like operating systems holding information about buses, devices, firmware, filesystems, etc.
• wikifs – a server application for Plan 9’s virtual, wiki, file system
• WinFS – Windows Future Storage, was planned as the successor to NTFS for Windows Vista.

File system interfaces

These are not really file systems; they allow access to file systems from an operating system standpoint.

• FUSE (file system in userspace, like LUFS but better maintained)
• LUFS (Linux userland file system – seems to be abandoned in favour of FUSE)
• VFS Virtual Filesystem
• Callback File System – the SDK to build custom filesystems and plug them to Windows OS.