flask: A lightweight Python framework that starts with Werkzeug and Jinja and scales to complex apps

Starting as a wrapper around Werkzeug and Jinja, it lowers the barrier to entry for Python web development. It provides a structure that flexibly scales to fit the size, from a simple Hello World to complex applications.

It does not require enforced project layouts or specific dependencies. It guarantees the freedom for developers to choose their own tools and libraries, and allows easy addition of needed features through community extensions.

It is an open-source project managed by the Pallets organization under the BSD-3-Clause license. With 73.1k stars, it has established itself as one of the most popular Python web frameworks.