CocoaPods trunk is moving to be read-only. Read more on the blog, there are 12 months to go.

MKBOSXCloseButton 0.0.1

You want to add pod 'MKBOSXCloseButton', '~> 0.0' similar to the following to your Podfile:

target 'MyApp' do
  pod 'MKBOSXCloseButton', '~> 0.0'
end

Then run a pod install inside your terminal, or from CocoaPods.app.

Alternatively to give it a test run, run the command:

pod try MKBOSXCloseButton

An NSButton subclass that looks just like the Yosemite+ native window close button