Thanks to hundreds of volunteers, QGIS is now a matured and powerful GIS and Software. And yes, it is FREE and open source. That means, at free of cost, you can perform almost any basic and advance GIS and Remote Sensing analysis with the software. In QGIS, you would get combined power of propitiatory GIS (i.e., ArcGIS, MapInfo) and Remote Sensing (i.e., ERDAS Imagine, PCI Geoomatic, ER Mapper, eCognition) software.
As of November 2016, latest version of QGIS is 2.18. This version is also called as ‘Las Palmas’. You can download the software from its official website www.QGIS.org. Installation is straight forward.
Learning curve of the software might be bit steep. But, you will find documentation in the same site to get started. Also search YouTube for introductory videos on QGIS.
There are hundreds of plugins which add additional capabilities to the software. Be sure to check those out.
Use QGIS and promote free and open source software movement.