SuperCard on Lion. And since I just wrote about HyperCard, its spiritual successor - SuperCard - still exists and has been made fit for Lion again. But it's still a Carbon application, so its days are probably counted (or it will become increasingly difficult to integrate SuperCard into current developments if a switch to Cocoa does not take place). And I'm still tempted to buy it, even if it's just for nostalgia. The hacking feeling of HyperCard I only experienced again later in Smalltalk environments (and they are unfortunately also rather dead under OSX).