Few if any cloud services can sync to a external HDD, this has been an issue for a long time... I was hoping BTSync would do it... the main issue is you can't get the required software to 'install' on the external HDD. (Think usb plug in drive or similar). The best I have found so far (for Windows) is SyncToy - but that needs to be scheduled to run periodically - it's not syncing as files are changed as cloud services and I assume BTSync does... Backing up to an external HDD is all very well, but it is not what most people want, nor do people want to have to manual transfer files to an external. So what is the simple tool that does this for you. I just want a straight replication of my chosen files and folders on my Hard Drive on an External Drive. If I can then sync further afield to other devices so much the better.