Today, just over a week since announcing iPhone 4S, Apple has made iOS 5 available for developers and users alike for iPhone 3Gs and later phones and iPods. This release brings integrated Twitter support, iCloud backup service for any application and user created documents, and PC free updating over the air of the operating system without needing a PC to perform the updates.
From a developer's perspective, iCloud and iMessage provide APIs which allow you to store data and communicate with other users, including the ability to start group chats from within an application (for example, enabling support mechanisms for instant feedback). Tweets can be posted from individual applications or using Twitter's URL shortening service. There are also developer tools to allow you to simulate a GPS trace for location oriented services, as well as new tools for detecting leaks.
Graphics support has been updated to OpenGL ES 2.0, along with GLKit, a new API for developing graphical games. The developer tools have also been updated to Xcode 4.2, which provides a number of improvements, including Automatic Reference Counting (or ARC) which allows you to provide a garbage-collected like codebase but with the performance of the reference counting without having to specify the retain/release cycles that many are currently familiar with. The AV Foundation libraries can allow your application to broadcast a stream to an Apple TV or other AirPlay device.
iOS 5 is available for immediate download, and developer documentation and downloads are available from the developer website for those enrolled in the developer programme.