Apple showed off iOS 5 during its World Wide Developers Conference keynote presentation on Monday. The next version of the iPhone, iPad and iPod touch operating system will include a redesigned push notifications system and a new iMessage messaging service, and drops the need to connect to a computer to activate devices.

iOS 5’s Notification Center

iOS 5, which will be shipping this fall, will include:

• Notification Center iOS 5’s Notification Center replaces the current push notification system with an interface that shows missed calls, calendar alerts, app alerts, instant message notifications and more in one place. Notifications no longer interrupt applications, and tapping a notification takes users to the apps they’re associated with.
• Newsstand Apple is mirroring its iBookstore with Newsstand. The feature lets users find, purchase and update digital newspaper and magazine subscriptions, and automatically updates subscriptions in the background.
• Single Sign-on for Twitter iOS 5 includes built-in Twitter support so that users don’t need to provide their account credentials to multiple client apps. Users can also post content to Twitter through Apple’s Photos, Camera, Safari, YouTube and Maps apps.
• Mobile Safari The mobile version of the Safari Web browser is getting the Mac OS X version’s Reader feature so users can view online articles as a single page and without extra layout features. It also includes an Instapaper-like Reading List feature that tags articles for later viewing, adds support for emailing article contents instead of just URLs, and adds tabbed browsing for iPad users.
• Reminders iOS 5’s Reminders feature adds task management to the iPhone, iPad and iPod touch. The app lets users track tasks, set alerts, track tasks by location, set priorities and due dates, and can be viewed in iCal or Outlook.
• Camera Apple’s Camera app gained the ability to take photos even when the screen is locked and use the Volume Up button as a shutter release. It also adds grid lines for easier photo composition, and the ability to set focus and exposure automatically with a tap.
• Mail The new Mail app offers encrypted message support, improved message searching, and rich text formatting. It also includes an improved portrait view, the ability to move email addresses between fields, support for flagging messages, and S/MIME support.
• PC Free Apple is dropping the need to connect iOS devices to computers running iTunes to complete the activation process.
• Over-the-air Software Updates iOS can now be updated without connecting your iPhone, iPad or iPod touch to iTunes. Updates will be delivered as deltas, meaning they include only changes instead of the full operating system.
• Game Center Apple’s Game Center is gaining support for user photos, in-app game purchases, turn-by-turn game support, and more options for locating new friends.
• iMessage iOS 5 is getting its own instant messaging service that’s available to iPhone, iPad and iPod touch users. It works over 3G or Wi-Fi connections, and supports text, video and photo messages outside of cell service provider’s SMS and MMS offerings.
• AirPlay Mirroring iPad 2 users will be able to show their display wirelessly through an Apple TV instead of relying on Dock to video adapters.

Apple also tightly tied its new iCloud online data storage and syncing service into iOS 5, so users only need to enter their Apple ID and password into their iPhone, iPad or iPod touch to wirelessly sync apps, photos, calendars, contacts, mail, music and more between devices.

iOS 5 will be available this fall at the same time as iCloud. The update will be available for free for the iPhone 3GS and iPhone 4, iPad and iPad 2, and third and fourth generation iPod touch.

[This article has been updated with additional information about iOS 5]