Flask libs I like
Flask-SQLAlchemy is an extension for Flask that adds support for SQLAlchemy to your application
http://flask-sqlalchemy.pocoo.org/
Flask-Allows is an authorization tool for Flask inspired by django-rest-framework's permissioning system and rest_condition's ability to compose simple requirements into more complex ones.
https://github.com/justanr/flask-allows/
Flask-HTTPAuth is a simple extension that simplifies the use of HTTP authentication with Flask routes.
https://flask-httpauth.readthedocs.io/
Flask-Login provides user session management for Flask. It handles the common tasks of logging in, logging out, and remembering your users’ sessions over extended periods of time.
https://flask-login.readthedocs.io/
The Flask-Mail extension provides a simple interface to set up SMTP with your Flask application and to send messages from your views and scripts.
https://pythonhosted.org/Flask-Mail/
Flask-Migrate is an extension that handles SQLAlchemy database migrations for Flask applications using Alembic. The database operations are made available through the Flask command-line interface or through the Flask-Script extension.
https://flask-migrate.readthedocs.io/
Simple integration of Flask and WTForms, including CSRF, file upload, and reCAPTCHA.
https://flask-wtf.readthedocs.io/
A Flask extension for handling Cross Origin Resource Sharing (CORS), making cross-origin AJAX possible.
http://flask-cors.readthedocs.io/en/latest/
Flask-RESTful is an extension for Flask that adds support for quickly building REST APIs
https://flask-restful.readthedocs.io/
Flask-Marshmallow is a thin integration layer for Flask (a Python web framework) and marshmallow (an object serialization/deserialization library) that adds additional features to marshmallow, including URL and Hyperlinks fields for HATEOAS-ready APIs. It also (optionally) integrates with Flask-SQLAlchemy.
https://flask-marshmallow.readthedocs.io/
Flask-Bootstrap packages Bootstrap into an extension that mostly consists of a blueprint named ‘bootstrap’. It can also create links to serve Bootstrap from a CDN.
https://pythonhosted.org/Flask-Bootstrap/
JWT (JSON Web Tokens) for Flask applications.
https://pythonhosted.org/Flask-JWT/
A Flask JWT extension that supports refresh tokens, blacklisting/revoking tokens, and token freshness (for accessing critical views)