Here is a list of public domain (or shareware) software that you might find to be of use.

arguslab - includes a builder, nice graphics, force fields, semiemprical and HF electronic
                structure calculations

jmol -     displays structures; can read output files from several electronic structure programs and
������������ �can display structures, vibrations, orbitals, etc. .log files and can animate vibrations. Note
������������ �that this program is at "openscience.org" web page, where there are many other useful applications.

openbabel – this is a very useful program for converting between different formats for geometries,
������������� �including those for periodic systems (version 1.6 is the last version that supported Gaussian z-matrices)

gamess - a very flexible electronic structure package

webmo – builder plus viewer, that interfaces with several electronic structure codes

molden – very useful for viewing orbitals, charge densities, etc. (ca build structures using z-matrices)

molworks – nolecular builder and viewer

jmoleditor – molecular building and other capabilities

pymol – a very useful viewer, animator