A "public suffix" is one under which Internet users can (or historically could) directly register names. Some examples of public suffixes are com, co.uk and pvt.k12.ma.us. The Public Suffix List is a list of all known public suffixes.

The Public Suffix List is an initiative of Mozilla, but is maintained as a community resource. It is available for use in any software, but was originally created to meet the needs of browser manufacturers.

An app that uses RDAP to collect publicly available info about domains, track their history, and purchase them

Open Source Domain Management Software.

DomainMOD is an open source application written in PHP used to manage your domains and other internet assets in a central location. DomainMOD also includes a Data Warehouse framework that allows you to import your web server data so that you can view, export, and report on your live data. Currently the Data Warehouse only supports servers running WHM/cPanel.

WebOSINT is a Python script to gather (passive) domain intelligence.