Hit: Steve Jobs introduced iCloud in June 2011 at Apple's Worldwide Developer Conference. A cloud-based storage and synchronization service, iCloud has plenty of competitors, including Amazon Cloud Drive, Dropbox, Google Drive, and Microsoft SkyDrive. No cloud service is perfect, of course, and iCloud is no exception. A two-day glitch last month prevented a small percentage of users from accessing their email, and similar mail-related problems popped up last summer. But for the majority of Apple, iCloud appears to be reliable and invisible so far--and that's one less headache for Tim Cook and team.