The new Today view in Notification Center gives a quick look at widgets for Calendar, Weather, Stocks, Reminders, World Clock and social networks; Spotlight now appears in front and center on the desktop and adds new categories of results; iCloud Drive stores files of any type in iCloud and searchable through the Finder; improved Safari browser and Mail app; new Messages user interface; and continuity features like Handoff that lets you stop an activity on one device and continue it on the other.
In addition to the visual enhancements, Apple has also brought many changes under the hood, allowing easier development of Mac apps. Yosemite adds support for SpriteKit for realistic motion, physics and lighting in games along with SceneKit for 3D casual gaming
Mac Developer Program devs can get the developer preview of Yosemite from today and will also allow end users to participate in the OS X Beta Program to try out the final version and submit their feedback.
