QGIS which stands for Quantum GIS, is an open source geographic information system that can be downloaded free.
ESRI vs QGIS
QGIS compatibility with ArcGIS: both can handle the most common spatial data formats however QGIS consumes all types of data formats. In terms of functions extensibility, both QGIS and ArcGIS functionality can be extended through plugins and extensions respectively. Each software has support system through user community and ArcGIS has technical support system for its products. Read more>>
Comparison of GIS functions and which software is best suited
For a more detailed comparison follow the links below:
Advanced functions that can be done with QGIS rather than ESRI Advanced Licence: in the absence of the right extensions or advanced license of ESRI, below are some of the functionalities that can be done with QGIS:
Functions
QGIS
ArcMap
Erase: creates a feature class by overlaying the Input Features with the polygons of the Erase Features.
Use the geoprocessing tool Difference.
You can access it through Vector>Geoprocessing Tools> Difference
Erase tool is available only with advanced ESRI license
Zonal Statistics: calculates statistics on values of a raster within the zones of another dataset.
The most common function IMOs use this tool is to extract population density from WorldPop image by COD-AB
In QGIS, the Zonal statistics tool which is located under the Raster Analysis toolbox does a similar function just like the ArcMap
See the link for steps
In ArcMap, Spatial Analyst extension is needed to carry out zonal statistics functions.
See the link for steps:
Hill shading of Digital Elevation Models (DEM)
Most used to enhance three-dimensional appearance of reference maps.
QGIS allows to visualize elevation data as hill shade without the user needing to create a separate hill shade raster.