What is SynoManager
SynoManager is an application you can install on your pc to control your Synology NAS device.
Currently it only helps you controlling the Download Station, but in the future it will also be able to control other aspects of your device, like the Audio Station or even the Management Station.

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Screenshots
List of Supported Devices
At the moment all of the Synology NAS devices (DiskStation, CubeStation and RackStation) are supported.
You have to make sure though, you have (at least) the 0722 firmware revision installed.
See also the SynoManager thread on the Synology Community Forums:
http://www.synology.com/enu/forum/viewtopic.php?f=38&t=4894