Showing it's new features, improvements and some... borrowed stuff from other OS's.
Apple also announced it's new version of the Mac OS X, 'Yosemite'. iOS 8 gives you the ability to interact with version of the Mac OS X. The feature is called Handoff, an expansion to the existing Airdrop feature of iOS 7. Handoff enables you to share a multitude of tasks and data,including phone calls, messages, photo and so on to the Yosemite.
Apple integrated a cloud drive feature to the iOS 8, and it will compete to other Cloud Drives like the Google Drive, DropBox etc. iCloud allows you to sync application files across all of your Apple Devices.
It's been a long requested feature from the user's of the iOS, and now Apple has added it to iOS 8. Though it would only accessible from the Notification Center and you are still would not be able to add widgets on your homescreen.
iOS 8 also enables you to quick reply on Messgaes directly from your Notification Center, saving you a little more time instead of opening the messaging app or switching to it.
Third Party Keyboards
iOS 8 now allows you to install and use Third-Party Keyboards, meaning Applications like Swiftkey and Swype would soon make it's way to iOS.
iOS 8 would feature it's own health monitoring app also, which has been a trend this year for Smartphones. Apple would be teaming up with a number of partners like Nike and Mayo Clinic for hardware.
The iMessage application has been improved gaining the ability to send audio and video messages.
TouchID for other Applications
Application makers would be able to utilize the TouchID feature for their own applications. Of course this features may only be used on the iPhone 5S and all upcoming iDevices that has a finger print scanner integrated with them.
Photos app improvements
The photos app of iOS is also improved allowing you to share photos to all synced devices.
AppStore improvements and New Features
The AppStore has been also improved, Search feature,App Bundles, Embbeded Videos,in app Descriptions and developes are now also able to invite users for their beta testing events.
This feature allows up to Six Users to share iTunes, iBooks and AppStore Purchases. Also Family photos, Calendar Events and locations are shareable also.
Availabilty of iOS 8
The iOS 8 would now be able to Beta Testers and the official release to all devices would be Fall this year. iPhones from 4S onwards would be the one to recieve the update, meaning the iPhone 4 would no longer be supported. iPads from iPad 2 and onwards are the to be supported and in the iTouch, only the iTouch 5 would be given the updated OS.