The Tag Clouds in BookMacster and Bookdog use my replacement for NSTokenField, which I have named RPTokenControl after Robert Pointon's Tag Cloud NSView, on which it is based.
The download includes a demo project (also based on Robert's). The code you would need to include in your project is all in the subfolder RPTokenControlKit. Visit this project's GitHub Repository to get it. Here's a video demo (4:12).