Resilio Sync allows you to automatically sync files between computers via secure, distributed technology (P2P bittorrent protocol).
With Drive File Stream, you stream your Drive files directly from the cloud to your Mac or PC, freeing up disk space and network bandwidth. Because Drive files are stored in the cloud, any changes you or your collaborators make are automatically updated everywhere.
This doesn't exist as a separate product any longer and just became Google Drive by the looks of it.
Gladinet Cloud Desktop mounts cloud storage to your local desktop PC. It is a simple desktop application.