R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, ...) and graphical techniques, and is highly extensible. The S language is often the vehicle of choice for research in statistical methodology, and R provides an Open Source route to participation in that activity.
For additional information, please refer to: The R Project: LSU Overview.
SPSS is a modular, tightly integrated, full-featured product line for the analytical process-planning, data collecting, data access, data management and preparation, data analysis, reporting, and deployment. The SPSS software is made available under the Louisiana State University license agreement with SPSS.
For additional information, please see: SPSS Statistics: LSU Overview.