Yosemite is a milestone in the development of OS X, a product that John Siracusa has been reviewing for Ars Technica since 1999. Learn what’s new in Yosemite: iOS integration, Extensions, application changes, iCloud Drive, and, of course, the bold new look. This is not a how-to guide; it’s a review of the operating system that explores the technologies and philosophies behind the features, all within the historical context of the Mac platform.