This page provides links for using Esri products on Apple computers.
ArcGIS Explorer is a freely available lightweight GIS data viewer from ESRI that lets you perform a variety of basic GIS functions. With ArcGIS Explorer, you can display, query, and retrieve data. Explorer may require access to an Enterprise version of ArcGIS Online.
ArcGIS Online lets you create maps within your browser and share them through embedding, email and more. If you are a current student, staff or faculty at Dartmouth, you have access to ArcGIS Online.
The UNH Cooperative Extension used to have a course called "GIS on Pennies a Day." They no longer have that course, but here is a short list of GIS software that is freely available. You should verify that it will work on a MAC computer.