Search for a GUI tag component such as OSX Cocoa NSTokenField for .NET / Ruby / Java

Question

I am looking for an input text box for tags, with autocomplete and highlighting, sort of like a Delicious.com tag input box. See the Tag Entry Window in the screenshot.

I know that Cocoa has its own GUI component, for example, such as NSTokenField. I need versions for Windows and OSX for my application, so I'm looking for something similar for Windows, preferably .NET, Java SWT or Ruby.