Infragistics released their design pattern browser Quince – based on Silverlight – some months ago. It´s focused on user experience design patterns and gives everyone the opportunity to read and to publish UX patterns.
What I really appreciate about this tool is the access it offers: you can search for patterns by keywords or explore all patterns, by user task, by tag relations, and by wireframe.
Check out the Interactive Pattern Viewer – there´s already a lot to discover =)
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Pattern Browser