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.

Download GRASS

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