GNOME 2.0 Human User Interface Guidelines
http://developer.gnome.org/projects/gup/hig/

Gnome.org
2003

Abstract:

This document tells you how to create applications that look right, behave properly, and fit into the GNOME user interface as a whole. It is written for interface designers, graphic artists and software developers who will be creating software for the GNOME environment. Both specific advice on making effective use of interface elements, and the philosophy and general design principles behind the GNOME interface are covered.