GRASS GIS is an open source GIS software which contains many funtionalities in ratser and vector GIS. Many functions performed by QGIS are actually throuhg GRASS GIS. When you download QGIS, an option is to download GrASS GIS at the same time. For business geography/business GIS, the most relevant part is the network analysis functions of GRASS GIS.
Getting started with GRASS GIS
Other GRASS GIS tutorial sites
https://grass.osgeo.org/documentation/tutorials/
http://www.ing.unitn.it/~grass/docs/tutorial_64_en/htdocs/esercitazione/datum/index.html