GMT has not been ported to the Macintosh platform. It is unlikely to happen until the Mac operating system provides a simple command interpreter with ability for standard i/o redirection. In the mean time you may use MkLinux or MachTen. The next generation MacOS X will provide some relief: The MacOS X Server was released in March 1999 and is built on a BSD UNIX implementation that will allow users to install GMT or any other UNIX package. The server version costs USD 499 (USD 299 for academics). On the other hand, the MacOS X user version (i.e., the version installed on new Macs you purchase) will not be ready until later this year and may or may not provide a command prompt. You may find out the status of these issues by checking the latest news at macUNIX.