I am making an open-source software that is an alternative version of another very popular software, Postman. The inspiration reflects mainly on user interface and concepts. No source code was copied from this software, I wrote my own entirely.
I searched about copyright licenses and their terms of service say (Section 8):
You and your Users shall not: (...) create any derivative works based on the Services;
and also (Section 4):
You acknowledge and agree that Postman (...) have and retain all legal right (...) in the Services including but not limited to any ideas, concepts, inventions, systems, platforms, interfaces, tools, utilities, user interface, algorithms, logic, formula, scripts, work flows, processes, software, (...)
However, it gets more complicated because some parts of their code are open-source on GitHub, under Apache license.
This related question answer argues that "Copyrights are about the actual source code, not about the ideas/concepts that are represented in that source code."
Am I infringing their license by creating my software?