CEO Tim Cook took the stage at 1 p.m. ET at Apple’s annual Worldwide Developers Conference in San Francisco to welcome a crowd of a few thousand software developers – some of whom had lined up a day earlier to ensure themselves a spot in the audience.

After a brief introduction, Cook handed the reins to Apple’s senior vice president of software engineering, Craig Federighi, who walked through the design and functions of Yosemite, which he called “a gorgeous and more usable version of OS X, the best ever.”

The new operating system includes design updates such as new desktop icons as well as a “dark mode” that switches menu bars and the dock to a darker gray color. Yosemite also includes an updated Notification Center and a faster, simplified Spotlight feature for searching for apps on your Mac and for searching online.

Federighi also unveiled the new iCloud Drive that will be available on Yosemite and will allow for the storage of content across all Mac and mobile products. The AirDrop feature will also allow for syncing between Macs and iOS devices, and it also includes “proximity awareness” – a feature that allows users to move documents and projects from device to device with the swipe of a finger.

Federighi used another new feature – the ability to answer phone calls on your Mac, using the computer as a speakerphone – to welcome one of Apple’s newest employees, rapper and Beats Electronics cofounder Dr. Dre. Federighi called Dre from his Mac and introduced him to the crowd, prompting the rapper to ask how early in the morning he should show up for work.

Yosemite will be available to consumers in the fall, and will be free. Those eager to try it out sooner than that can take part in a new public beta program.

More announcements regarding an updated iOS platform and other software products are expected later in the keynote address.

The five-day conference will be attended by 5,000 developers, who were chosen at random in a lottery to get access to the various sessions and labs Apple will run to help the developers familiarize themselves with new technologies. Later today, Apple will also give out its Design Awards to the developers of what the company deems to be the best apps available in its store.