ActiveSync is a data synchronization software developed by Microsoft for use with its Windows OS, excluding Windows Vista where it is replaced with Windows Mobile Device Center.

For the first time ActiveSync was released under the name “Handheld PC Explorer” in 1996. It provides transporting documents, calendars, contact lists and email between PC and a mobile device, such as PDA, mobile phone, smartphone, communicator or any other portable device that supports the ActiveSync protocol.

It works with the following mobile operating systems: Windows Mobile, Windows CE, Palm OS, Symbian.
In order to sync email, contacts, notes and tasks from your PC you must use MS Outlook 2002, Outlook 2003, or Office Outlook 2007.

ActiveSync supports not only wired connection through USB port and device’s cradle, but also wireless, over Wi-Fi.

Active Sync is a totally free software and usually comes on CD with the new mobile device.
Also it’s available for free download from Microsoft’s web site. The current version is 4.5.