Apple has re-engineered OS X 10 completely. Menubars are now translucent, reflecting iOS. There is also a brand new icon set, featuring gorgeously flat iconography. In addition, there is now an optional dark mode for people who don’t want to be distracted by OS X’s default white bright interface.
Apps have been reworked, featuring translucency and flatter materials throughout. Notification Center, for instance, flies in from the side with glossy blurs, very reminiscent of OS X.