A collection of usability guides for GUI designers

These are a collection of documents which provide guidelines to usability specialists, user interface designers and visual designers. If you are designing a user interface or a software for a particular platform, it will do you good to read the relevant document from this collection.

• Apple Human interface guidelines - Apple has developed one of the most popular user interface in Aqua. These guidelines are designed to assist you in developing products that provide Mac OS X users with a consistent visual and behavioral experience across applications and the operating system.
• GNOME Human Interface guidelines 2.0 - 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.
• KDE 4.0 Human Interface guidelines - These are a part of an important set of documents which describe how KDE applications behave and look. The guidelines document knowledge gathered by KDE developers as well as experts in the various fields that these guidelines touch.
• Sun Web applications guidelines 4.0 - This document was created by a set of user interface designers, usability specialists, and visual designers at Sun Microsystems to outline a usable web application look and feel that can be followed consistently throughout a product line.
  
• How to develop an effective GUI standard [PDF] - This is an online book which provides visual tips on how to do standardization while designing a GUI.