The app is robust, connects seamlessly at startup and does not crash. The app can map cloud storage as a local drive as well as a folder on a local drive, thus obviating the need to have free drive letters. The app displays the amount of used and free space and makes it easy for the user to see how much storage is available on each cloud account.
RaiDrive - Mount NAS, Router, Google Drive, OneDrive and Dropbox to a network drive or file explorer.
GoodSync - GoodSync provides highly reliable file backup and synchronization for both individuals and businesses.
Air Explorer - Air Explorer is a software to manage all your multiple cloud drives (like Dropbox, Onedrive, Google Drive, Mega, Mediafire, Box, Hidrive, Yandex, Baidu,...) as well as WebDav and FTP connections.
FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.
Mountain Duck - Cyberduck for mounting volumes in the file explorer. Available for Mac and Windows.
rsync - rsync is a file transfer program for Unix systems. rsync uses the "rsync algorithm" which provides a very fast method for bringing remote files into sync.