The final piece of software unveiled at WWDC today was iCloud, an exciting remix of MobileMe with a ton of new features and one very important change.  But what exactly is it?  Apple CEO Steve Jobs summed it up perfectly – as usual – in one of his trademark soundbites, describing iCloud as ‘storing your content in the cloud and pushing it to all your devices, automatically’.

The simplest example of what iCloud does is to imagine entering a new contact on your iPhone, and it being synced with the cloud and updated on all your devices, without any prompting from you.  This works with calendars, apps and mail too.  Any @me.com email accounts will have their inboxes and folders kept up to date across all devices this way too.

Because iCloud is integrated inside the standard iOS apps, there’s nothing to learn and very little to setup, making it very accessible for every user no matter what their level of expertise.  But the most important change?  iCloud will be free!

It isn’t just about your mail and calendar either, as other apps will work alongside iCloud too.  All apps will be synced across new devices, and each app can be re-downloaded via a purchase history (an existing feature we know, but this sounds much more obvious), plus an entire backup of your device will be synced to iCloud once a day, with everything from photos and music to bookmarks and settings saved.

If you use Pages, Keynote or Numbers, any new document will be pushed to other devices with those apps installed as soon as it’s closed.  Photo Stream will automatically sync any pictures taken with your iPhone to your iPad, iPhoto, Apple TV and even the Pictures folder on a Windows machine.  Older photos can be imported too.

Finally, iTunes in the Cloud lists all the songs you’ve purchased and allows you to re-download them on multiple devices, with no extra charge.  There’s also the option to push any new purchases to the cloud, where each file will be a high quality 256kbps AAC recording.  iTunes Match helps you with the music you’ve not purchased from iTunes, and for $25 per year you can upload any songs Apple can’t identify to the cloud, where they’ll be converted into 256kbps AACs.

iCloud will be out at the same time as iOS 5, and users will get 5GB of free storage.