Apple CEO Steve Jobs has briefly emerged from a medical leave to unveil a storage service that promises to let customers share contacts, calendar events and other data among devices more easily.
The company also announced new software to make Mac computers behave more like mobile devices and Apple's mobile devices more like rival smartphones.
Jobs received a standing ovation as he appeared at Apple's annual developers' conference, his second major public appearance since he went on medical leave in January for unspecified reasons.
Jobs left many of the specific announcements to top executives. In the first hour, he appeared on stage for only a few minutes.
James Brown's I Feel Good played over the loudspeakers just before Jobs walked on stage, looking thin, in his signature outfit of mock turtleneck and blue jeans.
One audience member shouted out: "We love you."
Jobs returned to stage about 80 minutes into the presentation to announce a service called iCloud. It will be free for now and replaces a 99 dollar (£61) a year Apple service called MobileMe, which Jobs said "was not our finest hour".
An iCloud account will store user information from several devices, including iPhones and iPads, and make sure the same contacts, calendar events and files are available on all of them. It also backs up the data on Apple's servers. It mimics Google's Docs system for online files, and products from smaller online-storage companies like Dropbox.
The iCloud service is also expected to allow customers to store their music online. The company has been in talks with the major recording companies to make this possible.
Apple did not announce a new iPhone model, as it usually does in June or July. The new version is expected to come in the autumn.