PALLETS/FLASK ? reverse-engineered prompt

Build me a lightweight Python web framework that makes it really easy to start a small web app and still grow it into something bigger later.

I want the basic experience to feel simple, so someone can create an app, add a route, and return a plain string or a rendered template with very little code. It should support the usual web app basics like request handling, routing, templates, and running a local development server. Keep it flexible, so people can choose their own project structure and add extra features later if they want.

Please include a tiny example app and make sure the setup and docs are friendly for beginners. If you need to look up current Python packaging or web framework best practices, do that. Also make it well tested and easy to contribute to, since this should feel like a real open source project.