- This is a tool to build binaries for Python applications. It could have just as been written in any other language that can produce binaries.

- Yes that is correct, applications are configured at build-time with environment variables. For example, you could use just 2 environment variables like in that demo to build binaries for sqlite-utils. There are a bunch of examples of common use cases here: https://ofek.dev/pyapp/latest/examples/

As far as how this works at runtime, I won't be able to explain any better than this Mermaid diagram I made: https://ofek.dev/pyapp/dev/runtime/#initialization