Windows 10 version 1809 has introduced the “Projected File
System” feature, only for NTFS physical drives and only for 64-bit applications.
Although this technology is not strictly related to Shell
Namespace Extension development (in fact, it’s not even related to the Shell,
it operates at the lower File System level), ShellBoost provides some exclusive
support for it, in combination with Shell Namespace Extension development, through
the ProjectedFileSystem and ProjectedFileSystemProvider classes.
The Windows Projected File System (ProjFS)
allows a user-mode application called a "provider" to project
hierarchical data into the file system, making it appear as files and
directories in the file system. For example, a simple provider could project
the Windows registry into the file system, making registry keys and values
appear as files and directories, respectively. An example of a more complex
provider is VFS for Git, used to virtualize very large git repos.