The Amion desktop scheduler (OnCall) runs under all versions of Windows. With a Mac, you can run the Amion Scheduler inside any program that sets up a Windows environment on the Mac, including Parallels, VMWare Fusion, and SoftWindows.
Installing the Amion scheduler...
If your browser allows it, run the program. It's called OnCallTR. Otherwise, save the file and then run it. A setup dialog should appear. Click Extract in the lower left.
A folder with a single icon will appear. Double click to start OnCall. To create a desktop shortcut, right click on the icon and choose Copy; right click on a blank spot on your desktop and Paste. Or you can always restart OnCall via the Windows Start menu; click All Programs and find the OnCall Scheduler.