Matrex is a lightweight vectorial spreadsheet. It calculates blocks of values, not single cells. It is strongly multi-threaded. Users can work together on sheets using a server. It has adapters to MATLAB, Scilab, Octave, and R.
Information regarding Project Releases and Project Resources. Note that the information here is a quote from Freecode.com page, and the downloads themselves may not be hosted on OSDN.