Sometimes "Because I can" just has to be a good enough reason to do something. That must have been what was going through the mind of Nick Lee, a developer who successfully put a 20 year old Macintosh operating system onto his Apple Watch. At the same time, it's a fantastic example of how far computers have come in the last two decades, both in terms of computing power and physical size.
In the video below, which was posted by MacRumors, you can see the result of Lee's work. He successfully runs OS 7.5.5 via the Mini Vmac Macintosh emulator which he has ported onto the watch. If you actually used one of those classic Macintosh computers back in the day be prepared for a moment of nostalgia, or possibly pain, when the computer smiles back at you. You can't really see it on the small watch screen, but you know what it's doing.
The only issue appears to be that since the Power PC operating system was not optimized for touch screens, you can't actually do anything with it once it loads. It just sits there and stares at you. Still, a bunch of hackers out there are upset they didn't think of it first.
The OS was originally designed for the Mac Power PC line in 1996, a computer which has a size advantage on an Apple Watch by an order of magnitude. Seeing that you can now run software on your wrist, that once required a desk, is an amazing thing to see. It may not exactly be a proof of concept of Moore's Law but it certainly says something about how far computing power has come and how quickly we've arrived there.