Quantum GIS is a user friendly GIS software, it runs on Linux, Unix, Mac OSX, and Windows and supports numerous vector, raster, and database formats and functionalities.QGIS has alot of features similar to ARC such as identify/select features,feature labeling, scale bar/north arrow etc. Also in QGIS you can view and overlay vector and raster data in different formats and projections without conversion to an internal or common format. This software was developed by Gary Sherman began in early 2002, For Mac users, the advantage of Quantum GIS over Grass GIS becauseit does not require the X11 windowing system in order to run, and all around the interface is much cleaner and faster. QGIS offers a selection of plug- ins to better increase the preformance of the free QGIS software, in reviews the QGIS user is satisfied with the product except for the lack of some tools but for a free program it is surprisingly versartile and has some good tools as well for example the editing tools make it simple and easy to create and edit projects.Quantum GIS is available free on their website.