Clearlooks is a theme for GTK, the main widget toolkit used by the GNOME desktop environment.
It is based on Red Hat's Bluecurve theme.
The creators of the Clearlooks GTK+ theme were Richard Stellingwerff and Daniel Borgmann; however, since 2005 the theme has been developed by GNOME, and current developers are Andrea Cimitan and Benjamin Berg.
Qt, versions 4.2 to 4.4, use a port of Clearlooks called Cleanlooks to better integrate with GTK applications.
Furthermore, a user by the name of jpfleury on Gnome-Look has recreated Clearlooks for GTK+ 3, called Clearlooks-Phenix.