They provide an installation method.

For servers, you can just run the daemon. For desktop, Nautilus is supported (or you can just run the daemon!).

https://www.dropbox.com/install-linux

For Dropbox? You install the official Linux client. For Google? There are third-party sync products and Gnome can mount it as a network drive but I didn’t mean to imply that I did; I don’t sync Google Drive with Linux.