This is the GNOME Virtual File System.

GnomeVFS is a filesystem abstraction library allowing applications
plugable transparent access to a variety of "real" filesystems, from
WebDAV to digital cameras, to the local filesystem. It also contains a
number of other convenient file utilities such as a comphrehensive MIME
database / Application registry, and a copy engine. Use of GnomeVFS
ensures that an application or component will be usable by Nautilus or
other GnomeVFS applications for handling the display of data from
various URIs, as well.

WWW: http://www.gnome.org/