QGIS (Quantum GIS) is a cross-platform free and open-source desktop geographic information system (GIS) application that supports viewing, editing, and analysis of geospatial data. Developed by OSGeo, Open Source Geospatial Foundation
License: Open Source
GRASS GIS (Geographic Resources Analysis Support System) is a geographic information system (GIS) software suite used for geospatial data management and analysis, image processing, producing graphics and maps, spatial and temporal modeling, and visualizing. It can handle raster, topological vector, image processing, and graphic data. Developed by GRASS Development Team
License: Open Source
GRASS GIS is a powerful tool favored for its advanced analytical capabilities, especially in raster and vector processing, but it has a steeper learning curve. QGIS, on the other hand, offers a more user-friendly interface with extensive plugin support, making it suitable for both beginners and experienced users.