Peter Merholz (of peterme.com) wrote about Zooming User Interfaces, making particular note of PAD++ implementations, which are indeed quite cool. I couldn’t help but remember Apple’s old Hotsauce project, AKA Project X. It was certainly one of the first examples of something along these lines, and interestingly enough continues to live today, in a way. For an update, visit this note by Brian Duck. It dates back to 1999 and describes how Hotsauce mutated to become part of the RDF spec.