PocketMac is the Mac equivalent of the Blackberry Desktop Manager software for Windows and is a free download from the Blackberry web site.
Once installed, an icon will be added to the Applications folder:

When launched, the interface appears very much like the iSync application:

Selecting the Blackberry icon displays the options available for the device:

Selecting the Contacts tab allows you to specify which local address books on the Mac you wish to synchronise with the Blackberry handheld:

The Calendar, Notes and Tasks tabs display the same options.
The Bookmarks tab allows you to synchronise Bookmarks to and from the handheld with the Safari web browser. In order to write bookmarks to the handheld you will need to install a plugin on the device via the Install button:

The Email tab allows you to specify which Mail applications on the Mac you wish to synchronise email messages with from the handheld. By default the MacOS Mail application will be selected, but if Microsoft Entourage is installed that application is also supported.

The Redelivery tab allows you to use the PocketMac software as a desktop redirector. Again you can select from all supported mail applications including MacOS Mail and Microsoft Entourage.

The iTunes tab allows you to synchronise Playlists from iTunes to the handheld:

The iPhoto tab allows you to synchronise photograph libraries from iPhoto to the handheld:

The Connection tab allows you to edit the connection settings:

PocketMac also allows you to install applications onto the device via the Utilities menu: