GNOME Core Applications is a collection of approximately 30 applications that are packaged as part of the standard free and open-source GNOME desktop environment. GNOME Core Applications have the look and feel of the GNOME desktop; some applications have been written from scratch and others are ports. All GNOME Core Applications except Evolution feature the GtkHeaderBar. GtkHeaderBar is a widget introduced to GTK in version 3.10. It is intended to replace the Title-Bar and the Toolbar for Client-Side Decoration.