How to write Xcode plugins?

Where can I fi开发者_开发百科nd resource on how to write Xcode plugins? I don't want to write macros and project templates, but plugins that extend the IDE functionality like the ones that can be developed for Visual Studio - capable of displaying in their own window and accessing Xcode project data.

See following:
http://maxao.free.fr/xcode-plugin-interface/

Xcode does not have a public plug-in API.

maybe more up-to-date: https://github.com/phausler/XcodeAPI

found via Regexident's answer on Xcode 4 plugin development

You can install Alcatraz

And then open XCode -> Windows -> Package manager, search XCode plugin in Template tab.

Then you can start a new project with XCode plugin template in OSX category.