Best database to use?

I am looking for a versatile and secure (does not connect to the internet, or at least can be disabled from doing so) database. I intend to store in excess of 1TB, consisting of PDF, Word Documents, Audio & video files. I would like the interface to have primary categories then multiple subcategory options (so when you click the main files they spread through the options, like a tree graph effect). Sorry a bit difficult to explain... Has anyone got any good ideas or advice?