MIME Router handles mapping incoming attachments via mailhandler and routing them to the appropriate CCK filefield(s). MIME Router relies on the incoming media MIME type to determine the appropriate filefield to route incoming attachments to. There is no configuration necessary as MIME router relies on the configured CCK filefields allowed file types. MIME router iterates over the available filefields configured for use with mailhandler and drops incoming attachments into the first filefield that allows files of the given type.
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 8/9 support was added on 4.x branch. Release 4.0.0 is currently being utilized with a Drupal 9 installation (PHP 8.0) on a production site and is operational. There are still features remaining to finish implementation for and issues to fix there, but overall it's a good starting point.
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.