Mac OS X Yosemite is available as a free upgrade for Mac users from the Mac App Store. It delivers a new look to the Mac operating system and introduces Continuity features that let you hand off activities between Mac and iOS devices.

Yosemite also includes a new Today view, a redesigned Spotlight and updated versions of Safari, Mail, Messages and iTunes. It's been redesigned with a "fresh, modern look, while maintaining the power and familiarity users expect from a Mac," says Craig Federighi, Apple’s senior vice president of Software Engineering.

Yosemite includes amazing Continuity features that make your Mac and iOS devices companions. Handoff automatically passes what you’re doing from one device to another, like writing an email or surfing the web. Instant Hotspot makes using your iPhone’s hotspot as easy as connecting to a Wi-Fi network AirDrop now works between Mac and iOS, so you can share content across devices.

All the SMS messages that previously only appeared on your iPhone now can automatically appear in Messages on your Mac and all your iOS devices. You can even make and receive iPhone calls on your Mac.