The BSD-2-Clause license is so simple to understand!

On the subject of copyrights, licenses, and ownership, each person contributing to PySWMM (and the related projects) owns their contributions (not businesses or universities). That means that the contributors hold copyright on their code. The main exception is for contributions made by the US Federal Government Employees. These individuals contribute their code in to the public domain since it is unclaimable.

There is a natural circular dependency on copyright vs public domain codes among the codebases and, as required, each of the three projects articulates this information inside the license file.

These projects are community assets and the direction of the codebases and functionality is steered by a meritocratic process.