Apple unleashed a flurry of software news related to its Mac and iOS operating systems during its annual developers conference Monday.

Most significant was the unveiling of iCloud, Apple’s solution for synchronizing content such as photos, music and documents across multiple Apple devices.

iCloud is Apple’s big push into online storage and data synchronization, after its previously failed attempt with MobileMe. CEO Steve Jobs said the company is killing MobileMe, which cost $100 per year, and replacing it with iCloud, a free service for all Apple customers. It will debut with the release of the iOS 5 operating system, due this fall.

Apple also previewed new features in its upcoming Mac operating system, OS X Lion, which is looking more and more like iOS. Click through the photos above to see highlights from Monday’s keynote.