SAGA - short hand for "System for Automated Geoscientific Analyses" - is a free,
hybrid, cross-platform GIS software.
The heart of SAGA is its C++ and thus object oriented Application Programming
Interface (API), providing data object definitions and computational methods for
raster, vector and tabular data. As a normal user, you will not get into touch
with the API. But as an interested scientist or coder you will soon discover
its great flexibility.