open source software for CART and Principal Component Analysis

I need open source software, or however a free software (i would download 
and use it without pay!), for manage data with CART or Principal Component 
Analysis. Tipically Matlab is the best software solution, but it isn't free! 
GNU Octave is free but not more powerful! Then, please, could you help me? 
Thanks by the poor poor little italian student Leo! :)