Past is free software for scientific data analysis, with functions for data manipulation, plotting, univariate and multivariate statistics, ecological analysis, time series and spatial analysis, morphometrics and stratigraphy. It is a freeware data analyzing application that's well-designed, light on system resources, advanced and powerful.
Here are some screenshots to illustrate the features and user interface of this application:
GeoGebra
GeoGebra Portable
Qalculate
gnuplot
Maxima