Linux Journal profiles uDIG, a Java-based open source GIS application (the acronym refers to User-friendly, Desktop, Internet, GIS).   The article by James Gray reviews how to download uDIG, where to find GIS data and reviews the basic functionalities of loading data, symbolizing and selecting attributes.  James Gray also has an earlier overview of Quantum GIS (aka QGIS) which includes a similar process of reviewing where to download QGIS, accessing and basic functionality.

• uDig GIS: A First Look
• Quantum GIS: the Open-Source Geographic Information System