"Elementary OS has a rather unconventional history. It first
started out as just an icon theme. Shortly thereafter, it grew GTK+
and Metacity themes. Along the way came a mod for the Nautilus file
browser, default in Ubuntu and most other distributions with GNOME,
called Nautilus Elementary; I've mentioned that mod before here,
but for those who don't know, this mod organizes the side panel
items by category (Personal, Devices, Network), beautifies the
breadcrumb-style pathbar, removes some redundant navigation
buttons, and compacts the menubar into a button. Then, the project
started to expand its focus to include applications alongside
aesthetics, with the Postler mail client and the accompanying
Dexter address book program. Alongside these efforts came many
other mockups for various other applications, such as Mozilla
Firefox, Pidgin, Empathy, FileZilla, and others. More recently, the
Elementary developers created a new panel called the WingPanel to
replace the GNOME Panel on top, along with a new application
launcher called Slingshot, all combined along with all the other
applications into a new shell for GNOME called Pantheon."