X-Plore is a file manager for S60 phones from Lonely Cat Games the authors of Smart Movie and Profimail. X-Plore is currently available as a free beta. It includes the usual file manager features and also includes a images and text viewer. It does not use the standard S60 UI elements and consequently is able to fit more information on the screen at one time.
Because on Symbian operating system version 9 and later, system directories are protected from access by unprivileged applications. And there are no file manager/explorers with the required privilege (known as "AllFiles" capability).