Dropbox is a cloud based file storage and sharing service and it allows you to easily share files by just copying it to local folder. ZapDropbox is a freeware tool based on Dropbox which allow you to change the desktop wallpaper on multiple desktop using Dropbox. Once installed, you can set the folder in Dropbox where you want to keep all the wallpapers. Once you add the wallpapers to the folder, you need to make sure that the files are shared and public.
You can specify the time interval for changing the wallpapers, for changing the wallpapers remotely, you need to have an FTP app installed for accessing the remote PC. ZapDropbox can operate in “Independent” mode which is also the default mode. But the best feature is to configure mode “Client / Server”. Either using the same account Dropbox on multiple computers, or with several accounts and sharing a folder with friends and family.