Expect is a tool for automating interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, qemu etc. Expect really makes this stuff trivial. Expect is also useful for testing these same applications. And by adding Tk (tk), you can also wrap interactive applications in XWindow interface.
Expect can make easy all sorts of tasks that are prohibitively difficult with anything else. You will find that Expect is an absolutely invaluable tool - using it, you will be able to automate tasks that you've never even thought of before - and you'll be able to do this automation quickly and easily.