Is there a customized realtor sales and property management and contact prospecting system available for CiviCRM, eg through an extension or set of modules integrating with Drupal?
CiviCRM can be customized by developers and implementers to suit a wide variety of needs. It may or may not do what you need out of the box, but one of the CiviCRM Partner companies could help you out.
CiviCRM is the best open source CRM going and when used with a CMS like Drupal can be quite extensible and powerful.
I think that with CiviCase and other Activities and using Drupal Views and Webforms you could build a system to track leads and sale process quite well. While CiviCRM was designed for non-profits it is very adaptable and is used in a huge range of contexts. The flexibility of Activities and Case management provides great potential for such use cases.