After first acknowledging last week that it was launching a service called iCloud, Apple on Monday took the wraps off, during a two-hour keynote presentation kicking off this week’s Worldwide Developer Conference (WWDC) in San Francisco. iCloud is expected to be fully operational this fall with the release of iOS 5, though some features are available now.

[ad#Google Adsense 300×250 in story]iCloud is a set of free “cloud” services that enables users to synchronize data, apps, content, music and more between Macs, PCs and their wireless devices running iOS – iPhone, iPad and iPod touch.

The service incorporates the capabilities Apple previously offered under its subscription-based “MobileMe” service – e-mail, contacts and calendar synchronization, now re-architected to work with iCloud features. Users can share calendars; inboxes and mailboxes are kept up to date across all devices.

iCloud backup backs up iOS devices daily over Wi-Fi, securely and automatically. Backups include purchased music, apps and books, the contents of your devices’ Camera Roll, settings and app data. As you buy new devices, you can automatically restore all that content to the new devices during setup.

Both the App Store and the iBookstore will download apps and books to all devices rather than only the ones they were purchased on; you can download any apps and books you’ve bought to up to ten iOS devices.

iCloud Storage stores all documents; when any document changes on any device, iCloud pushes the change to all other devices. Pages, Keynote and Numbers – the apps included in Apple’s iWorks suite – already support this capability. Users get 5GB of free storage, and can buy more storage (details will be posted this fall, when iCloud formally debuts).

Photo Stream automatically uploads and and syncs the photos you take or import; the last 1,000 photos are stored in the cloud. Macs and PCs store all photos from the photo stream, and iCloud keeps each image for 30 days.

iTunes in the Cloud is the figurative icing on the iCloud cake – it lets you download previously-purchased iTunes Store-bought music to all iOS devices at no additional cost. And new music can be automatically downloaded to all devices.

For users with libraries full of music not purchased from iTunes, Apple offers iTunes Match, a service with a $24.99 annual fee. iTunes Match compares music in your library to what’s on iTunes; you can replace what’s on your computer with a 256kbps AAC-encoded DRM-free version if iTunes can match it.

By matching your content to what’s on the iTunes Store, you can sync the music to any authorize devices, potentially in minutes. If iTunes fails to find a match, you can upload the unmatched music, then sync it.

Apple is releasing on Monday a beta version of iTunes in the Cloud, without the iTunes Match service, for iPhone, iPad and iPod touch users running iOS 4.3. iTunes in the Cloud wil support all iPhones that support iOS 5 this fall.