Sails.js vs Flask

Sails.js is built with a focus on building real time communication apps such as chat or multiplayer games, so naturally it has Socket.io extremely well supported.

This could be a huge plus, if you prefer to build your apps using the Model View Controller architecture. Using Sails.js you'll find the task of separating the business logic from the user interface and keeping the interactions between them in a separate layer, extremely easy.

Exposes public JSON API for free. No additional routing to be defined. Makes it pretty easy to access data from anywhere.

Sails.js uses Waterline ORM at its backend which means you can store your data in any datastore that you like; all you have to do is make a change to the Waterline adapter, this will allow you to store your data in MySQL/Redis or any other kind of database.

Clear documentation and easy to understand. The file structure gives you a way to understand where you can start to develop when you encounter a new Sails project

Flask is very easy to get up and going, with vanilla HTML or with bootstrap pieces. It doesn't take much lines of Python to load Flask to get headers working, etc, and since it's all modular you don't have to have something you don't want in your application.

Flask is one of the most popular Python web frameworks, if not the most popular one. As such, there's plenty of guides, tutorials, and libraries available for it. A large number of important Python libraries, such as SQLAlchemy have libraries for Flask, which add valuable bindings to make the development process and the integration between these libraries and Flask as easy as possible.

Even though it's pretty minimalistic out of the box, Flask still provides the necessary tools to build a quick prototype for a web app right after a fresh install. With all the main components pretty much packed in the flask package, building a simple web app in a single Python file is as easy as it gets.

Flask gives developers a lot of flexibility in how they develop their web applications.

For example, the choice of not having an ORM, but instead choosing one suited to the task, or another area where Flask gives a lot of options to developers is the templating. They can use Jinja2, Flask's default templating language or choose from a number of different templating languages they desire.

The official documentation is very thorough and complete. Everything is explained in-depth and followed by extremely well-explained tutorials that tackle real-world problems.