I am searching for a Joomla or Drupal software product site theme(ideally Drupal and free)? I've not a problem when the theme needs some css hacking. Any suggestions?

Thanks

If you are selling the utility program and you are using Drupal, you need to use Ubercart. (take a look at http://ubercart.org and http://drupal.org/project/ubercart ).

A great theme enhanced for selling items is http://drupal.org/project/acquia_prosper

To obtain ready to go with acquia succeed and ubercart generally rapidly I would suggest the next project http://drupal.org/project/uberdrupal