Are you looking to sync all the services with an Egnyte domain or is it either of them ?
We do not have any integration available with OneDrive or DropBox, but yes, we do have an integration with GoogleDrive. You can simply look up Google Drive integration in our helpdesk and you will find relevant articles giving you more information. See if this suits your requirement.
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Re: Sync files between Onedrive/GoogleDrive/Dropbox and Egnyte
Is the Salesforce Report available to be saved back to Salesforce as either a "Notes & Attachment" or a "File" if that is the case we have a Salesforce integration that strips those files and puts them in the corresponding folder in Egnyte.