To write a single DSK image file you can either use :

• ManageDSK by Demoniak (windows)
• iDSK by Sid (it's an unix/macos port of ManageDsk, it seems that you will need the dsktools by Andreas Micklei)
• WriteDSK by Targhan (on Amstrad CPC only)
• CPCDiskXP by Mochilote (windows)

Beware, WriteDSK works on the CPC (you must have a PC 3,5" with the .DSK which will be copied on the same 3,5" drive or another 3" drive). It supports the CPC Booster by Antitec.

But if you want to write a double sided DSK, you will have to use CPCDiskXP by Mochilote for the moment.

P.S. : from the WriteDSK documentation, it should support double side DSK.