Open Source Software
Free and Open Source Software for Geospatial (FOSS4G) is widely used across the world, and allows users to access spatial databases and geospatial functionality without the need for licensing.
Functionality and speed rival that of commercial software as FOSS4G platforms have improved over the years, including but not limited to, QGIS, Postgres/PostGIS, and R.
QGIS is the go-to FOSS4G desktop GIS software. It has a similar style to ArcGIS with a display area and list of layers, as well as menus, buttons, and a toolbox for performing spatial operations. Much of QGIS’ power and functionality comes as plugins, so you can add just the functions you need.
PostGIS is a spatial database extender for PostgreSQL object-relational database. It adds support for geographic objects allowing location queries to be run in SQL.
It allows a user to store tabular and spatial data in a relational database, and perform spatial operations using powerful and SQL. The spatial SQL expressions directly access the shape field and can perform complex operations, including overlays, spatial joins, and much more.
Whitebox Geospatial Analysis Toolbox is an open-source desktop GIS and remote sensing software package for general applications of geospatial analysis and data visualization packed with hundreds of tools to clip, convert, analyze, buffer, manage and extract geospatial information.
GRASS GIS, commonly referred to as GRASS (Geographic Resources Analysis Support System), is a free and open source GIS software suite used for geospatial data management and analysis, image processing, graphics and maps production, spatial modeling, and visualization.
GRASS GIS is currently used in academic and commercial settings around the world, as well as by many governmental agencies and environmental consulting companies. It is a founding member of the Open Source Geospatial Foundation (OSGeo).