According to Apple, the developer preview of OS X El Capitan is available to Mac Developer Program members starting Monday. Mac users can participate in the El Capitan Beta Program in July and download the final version for free from the Mac App Store this fall.

iOS 9

"iOS 9 is packed with more intelligence throughout, and delivers big updates to the apps customers use most -- Maps supports public transit, a redesigned Notes app provides great new ways to capture ideas, and a beautiful News app delivers content that's personalized to your interests," said Federighi.

According to Federighi , with the new multitasking iPad features, users can take advantage of the power of iPad, working in two apps at the same time with Split View, Slide Over or Picture-in-Picture.

WatchOS 2

WatchOS 2, the first major software update for Apple Watch, unveiled during the WWDC, giving developers the tools to build faster and more powerful apps running natively on Apple Watch.

According to Apple, starting Monday, developers can take advantage of innovative hardware features of Apple Watch including the "Digital Crown", "Taptic Engine" and heart rate sensor, along with software APIs to build new app experiences.

"We are thrilled with the feedback we're getting from Apple Watch customers, and after just a few weeks of availability we're excited for developers to start building native apps for watchOS 2," said Kevin Lynch, Apple's vice president of Technology.

News app

According to Apple, "News" is an app that is powered by the new custom-designed Apple News Format, a digital publishing format that allows publishers to create beautiful layouts.

"News seamlessly delivers the articles you want to read in a beautiful and uncluttered format, while respecting your privacy, because Apple doesn't share your personal data," said Eddy Cue, Apple's senior vice president of Internet Software and Services.

According to Cue, the company already has nearly 20 publishers representing more than 50 titles joining the app, such as Condé Nast, ESPN, The New York Times, CNN and Bloomberg.

Apple Music

During the typical "one more thing" segment of Apple's event, Cook introduces "Apple Music", a single, intuitive app that combines the way to enjoy music -- all in one place.

According to Cook, Apple Music is a "revolutionary streaming music service", a pioneering worldwide live radio station from Apple broadcasting 24 hours a day and a great new way for music fans to connect with their favorite artists.

Apple Music combines the largest and most diverse collection of music on the planet with the expertise of world-class music experts who have programmed playlists for your iPhone, iPad, iPod touch, Mac, PC, Apple TV and even Android phones.

Apple Music will be available starting on June 30 in over 100 countries, said the company.