Apple ISync & .mac Sync
Apple's iSync synchronization software offers a wide range of synchronization options. Originally, Apple wanted to offer iPod users the chance to copy their address books to their iPods. Today the software not only syncs iCal-events (calendar items), it also supports almost 60 different target devices such as mobile phones, iPods and some PDAs. Third-party vendors offer software like "The Missing Sync" from Mark/Space to make devices compatible, which have yet to be acknowledged by Apple. Microsoft developed an update for Mac Office 2004 users to pass on Entourage data via iSync.
Apple's own list is refined constantly. The latest update OS X.4.6 added more devices to the list, Nokia's 6230 as well as the Motorola RAZR V3i are included. You can find the latest list of compatible devices at http://www.apple.com/macosx/features/isync/devices.html.
Whoever would like to synchronize a level above should use Apple's .mac Sync. This software allows you to distribute data at the internet/intranet level to other devices.
Mac OS X address book Contacts...
... and the entries in iCal calendar...
... can quickly be synchronized to external devices via iSync. Each device will be integrated in iSync according to the nature of its content and content organization (see Apple website).
.mac Sync does synchronization over the Internet or an intranet