It will transparently proxy your ftp clients (duh). This means that any
clients you have that are behind the proxy will believe that they are
connecting to an ftp server as normal, but will actually be connecting
to frox. Frox will do the onward connection to the remote server.

It can also be set up to do non-transparent proxying. In this case the
ftp client can connect directly to frox, but instead of logging in with
``username'' should log in with ``username@ftp.wherever.org''.

On either of these sorts of connections it can do caching of files you
download, or converting of data connections from active-->passive which
can make firewalling rules a lot easier/safer. There is also basic
support for running a virus scanner on downloaded files.

See http://frox.sourceforge.net/ for more information.