SPSS (Statistical Package for the Social Sciences) is a computer application that provides statistical analysis of data. It allows for in-depth data access and preparation, analytical reporting, graphics and modelling.
SAS (Statistical Analysis System) is a software package that has a number of functions including statistical analysis, report writing and graphics, data warehousing and data mining, plus much more.
Stata is a complete, integrated statistical package that provides everything you need for data analysis, data management, and graphics. With a point-and-click interface, an intuitive command syntax, and online help, Stata is easy to use, fast, and accurate. All analyses can be reproduced and documented for publication and review. For more details, see http://www.stata.com/