GRASS (Geographic Resources Analysis Support System), is a free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization.
A set of open source GIS binaries for Windows (win32) and Linux (x86 32bit) systems intended to be easy for end users to install and get going with. FWTools includes OpenEV, GDAL, MapServer, PROJ.4 and OGDI as well as some supporting components.
A desktop app for capturing, storing, handling, analyzing and deploying referenced geographic information to solve complex management and planning problems. It is known for having a user-friendly interface and being able to access the most common formats. It features a wide range of tools such as query tools, layout creation, geoprocessing, networks, etc.
System for Automated Geoscientific Analyses is an open source geographic information system used for editing spatial data. Its purpose is to give (geo-)scientists an effective but easily learnable platform for the implementation of geoscientific methods.
Tropical Storm Arthur. Image courtesy National Hurricane Center. Retrieved from Visible Earth.