Please read the copyright for Arc.

Arc does not run on a Macintosh as a standard Macintosh program with System X. Mac users have four choices:

• A package is available for installing Arc on Intel Macs with system 10.5 or later and X windows. X windows usually comes with the Mac but may not be installed. Once the package is downloaded to your desktop, simply double-click on it and follow the on-screen instructions. Then, after installing Arc, open an X window and type arc. The interface for Arc is a little different than on other machines, but the functionality is the same.
• If you have a Windows emulator, or if you have Parallels Desktop on an Intel Mac, www.parallels.com, you can install and run the Windows version of Arc on your Mac.
• If you have an older Mac with System 9, or an earlier version of System X that supports "classic" mode, you can use the installer Arc1.06Installer.sit.
• If you are a brave soul, you may be able to install Arc as a Linux program on your Mac. Here are instructions.