GGobi is an interactive, direct manipulation tool for visualizing high
dimensional data across linked plots.  It provides highly dynamic and 
interactive graphics such as tours, as well as familiar graphics such 
as the scatterplot, barchart and parallel coordinates plots.  Plots are 
interactive and linked with brushing and identification. The GUI is built 
using Gtk+.  It reads data in regular ASCII format and more richly using 
an XML format.  Plugins for other formats are also available.