The Drupal RETS Real Estate Framework (dRealty) enables administrator-developers to get real estate data via RETS and maintain a copy of that data in Drupal. dRealty is focused on that one-way data flow, and it does not include a user interface beyond administrative and configuration pages.
The Drupal 7.x-3.0 stable release is out (hopefully, with the only minor BUG overlooked: https://www.drupal.org/node/2840750#comment-11863587) and the support documentation and Video is to be produced in 2017.
The Drupal 8.x release is being designed, and the download is unusable and unsupported until further notice. If you would like to join the 8.x work then review the issue "Plan for dRealty for Drupal 8". The next hangout for coordination is scheduled to be April 22, 2016, at 1 pm ET.