Apple is celebrating a big milestone today, as its Mac OS X operating system turns 10. That’s 10 years since the first beta of the successor to Mac OS 9 was introduced. On the Mac side of things, OS X played a key role in the reinvention and reinvigoration of Apple, a company that had seen a lengthy stint of turmoil and trouble up to that point.

The first iteration of OS X, 10.0, was ironically named “Cheetah,” despite obviously being the slowest in the series now. After Cheetah came Puma, Jaguar, Panther, Tiger, Leopard and now, Snow Leopard. Each big cat nickname represented a major point update to the operating system (e.g., 10.1, 10.2, etc.). A screenshot below shows you what OS X 10.0 looked like, so you can see how far it’s come visually if you aren’t familiar.