Nuvola is a free software icon set under the GNU LGPL 2.1 license, created by David Vignoni.
[1] Originally created for desktop environments like KDE and GNOME, it is also available in packages for Windows and Mac.
The default set is in the PNG graphics format; an SVG version is also available.
The application icons, in particular, colourfully represent a wide variety of commonplace and easily recognised objects.
Besides KDE and GNOME, Nuvola is used by the Pidgin instant messaging client, the Amarok media player and the KeePass password manager.