Recommended and mentioned products
CloudMounter for Mac OS X: map Dropbox as network drive, mount OneDrive, Google Drive and Amazon S3; FTP client and WebDAV client.
Mount NAS, Router, Google Drive, OneDrive and Dropbox to a network drive or file explorer.
ExpanDrive is a fast network drive and browser for cloud storage.
WebDrive File Access Client allows you to open and edit server-based files without the additional step of downloading the file.
paid Free Trial $59.95 / One-off