QGIS - QGIS is a desktop geographic information system, or GIS.
PostGIS - Open source spatial database
GRASS GIS - GRASS GIS is a free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization.
H2GIS - A spatial extension of the H2 database. Compliant, Solid, Tested.
SAGA GIS - SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS)...
ArcGIS - ArcGIS software is a data analysis, cloud-based mapping platform that allows users to customize maps and see real-time data ranging from logistics support to overall mapping analysis.