A client is required to play empire. Here are a list of available clients with links for downloading. Note that most clients are donated from the Empire community at large. Also note that you CAN use, while rather ugly, plain old 'telnet' as a client by just telnetting into the HOST and PORT of the game.
If you don't see a client for your specific platform here, you can always try downloading the basic Empire client and building it for your platform. It runs on many versions of Unix as well as Windows/DOS. Note that as of version 2.8, the basic Empire client is released under the GNU GPL. See the associated tarball/archive for more details.
Some historical versions of clients are also available in our archive.