Flask's large ecosystem of extensions make it easier for developers to build common web app features such as authentication, relational database access and APIs even though support is not built into the core Flask library.

Specific examples are shown on the following individual pages, organized by classes and functions provided by Flask, that are frequently used when building your own web applications.

The following active projects use the Flask framework in various ways. The code within the projects can show you how to build your own applications.

Braintree's Flask example payments app demonstrates how to incorporate this payment provider's API into your Flask web application. The code is open sourced under the MIT license.

CTFd (homepage) is a capture the flag (CTF) hacking web app built with Flask. The application can be used as-is to run CTF events, or modified for custom rules for related scenarios. CTFd is open sourced under the Apache License 2.0.

The Datadog Flask app contains many examples of the Flask core functions available to a developer using the web framework.

The keras-flask-deploy-webapp project combines the Flask web framework with the Keras deep learning library to provide an example image classifier that is easy to deploy. The application can be quckly run in a Docker container on your local development environment. The project is licensed under the GNU General Public License v3.0.

FlaskBB (project website) is a Flask-based forum web application. The web app allows users to chat in an open message board or send private messages in plain text or Markdown.

FlaskBB is provided as open source under this license.

flask-bones (demo) is large scale Flask example application built with Blueprints (example Blueprint code). This project is provided as open source under the MIT license.

Flaskex is a working example Flask web application intended as a base to build your own applications upon. The application comes with pre-built sign up, log in and related screens, as well as a database backend. Flaskex is provided as open source under the MIT license.

flask-bookshelf is the example Flask application that developers create when going through this Flask series of blog posts.

Flask JSONDash is a configurable web application built in Flask that creates charts and dashboards from arbitrary API endpoints. Everything for the web app is configured in JSON. The code is provided as open source under the MIT license.

flask-phone-input is an example application that ties together the intTellInput.js JavaScript plugin with the Flask-WTF form-handling library. flask-phone-input is provided as open source under the MIT license.

flaskSaas is a boilerplate starter project to build a software-as-a-service (SaaS) web application in Flask, with Stripe for billing. The boilerplate relies on many common Flask extensions such as Flask-WTF, Flask-Login, Flask-Admin, and many others. The project is provided as open source under the MIT license.

Flasky is a wonderful example application by Miguel Grinberg that he builds while teaching developers how to use Flask in his books and videos. Flasky is open sourced under the MIT license.

indico (project website, documentation and sandbox demo) is a Flask-based web app for event management. The code is open sourced under the MIT license.

NewsPie is a minimalistic news aggregator created with Flask and the News API. NewsPie is provided as open source under the MIT license.

Science Flask is a Flask-powered web application for online scientific research tools. The project was built as a template for any scientist or groups of scientists to use when working together without having to really understand how the application is built. The application includes an academic registration process (only valid academic email addresses can be used), an admin panel, logging, and analysis forms.

@danielhomola is the primary creator of Science Flask and the project is open source under the GNU General Public License.

ShortMe is a Flask app that creates a shortened URL that redirects to another, typically much longer, URL. The project is provided as open source under the MIT license.

tedivm's flask starter app is a base of Flask code and related projects such as Celery which provides a template to start your own Flask web app. The project comes baked with an admin panel, API authentication and authorization, SQLAlchemy and many other common libraries that are often used with Flask.

The project's code is provided as open source under the BSD 2-Clause "Simplified" license.

trape is a research tool for tracking people's activities that are logged digitally. The tool uses Flask to create a web front end to view aggregated data on an individual the application is set to track. The source code is provided as open source under the MIT license, according to the README.