There are many GIS software options. You can begin with either ArcGIS (the proprietary industry standard) or free and open source software (QGIS being a popular choice). Each package has its merits and drawbacks. Most GIS data formats are cross platform and will work in any package.
Produced by ESRI, ArcGIS is the primary proprietary software on the market. It has a long development history, is powerful, well supported, and widely used. It is also expensive, resource intensive, and runs only on the MS Windows operating system. Brown has a site license for ESRI products: the software is available in labs throughout campus and can be downloaded by current members of the Brown community. Support is available from the EarthLab, S4, and the library.
There are a number of solid, well-developed free and open source (FOSS) GIS packages that provide a reasonable alternative to proprietary software. These packages run on Windows, Mac, and Linux. QGIS is the choice for most desktop GIS users and is recommended if you are learning GIS. Most of the other programs listed here can run either through QGIS or via stand-alone interfaces. Support is available from the library and S4.