The GNOME project (pronounced with a hard "G") is a collaborative software project building a complete, user-friendly DesktopEnvironment entirely from FreeSoftware components. Its most apparent distinction is that it's built on the GimpToolKit, which is licensed under LGPL (more business-friendly than KDE's Qt, which is available under either GPL or as commercial payware). Components of GNOME include GConf, Nautilus, a virtual FileSystem layer (gnome-vfs), and more.
GNOME is the DesktopEnvironment of choice for business Linux, adopted by the likes of IBM and SunMicrosystems. Much development on it was funded by Ximian, a company founded by GNOME initiator MiguelDeIcaza and later purchased by Novell. Novell have set Free most of Ximian's code, and the Ximian crew are now Novell's team for LinuxOnTheDesktop.