QGIS is an open source, freely downloadable and distributable professional desktop GIS package. It has an active developer and user community. It’s robust, well-supported and integrates extremely well with other open source tools such as PostGreSQL/PostGIS and GeoServer. As such it is a valuable component of your Spatial Data Infrastructure (SDI).
QGIS handles all standard GIS formats such as shapefile, KML and MapInfo TAB file, GeoPackage as well as many less well-used ones.
Fast developing, easy to learn, multi-platform, available in many languages
Heavily customizable, free and open-source (read: legal), lower TOC
Modular, with new components and modules being added every day
Stable, active user base, bugs fixed by community in short time
Fast and performs processes in a small amount of time than the proprietary equivalent