In the present chapter, you will be introduced to some very useful public domain software which helps in carrying out the common numerical tasks and also for plotting the experimental data. One is SCILAB which helps in numerical techniques and has a vast help menu. This can be downloaded in UNIX as well as windows environments. Another is the software Xmgrace which is excellent for plotting data and is presently available in UNIX. We have already used the software Graph 4.3 in Chapter 4 wherein we studied interpolation. Avogadro is useful software for plotting and viewing molecular clusters as well as large molecules. Gamess and Gromacs are very powerful software that are useful for doing ab initio calculations and bimolecular simulations respectively.  This list of public domain software will keep growing with time and you can search on the web for additional software. A useful website to know about the basic microscopic properties of a few molecules (such as energy, dipole moment, polarizability and so on)  is http://www.chemeddl.org/collections/molecules.