Sails is based on Express and Socket.io. It also takes advantage of Winston for logging, ejs for templating (configurable), and bundles felixge's Dirty RAM/disk database for getting up and running quickly without having to install mySQL or whatever.
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Pro JSON API generated for free
Exposes public JSON API for free. No additional routing to be defined. Makes it pretty easy to access data from anywhere.
Pro Transparent support for Socket.io
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.
Pro ORM that can be plugged into any database, or even custom web service
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.
Pro MVC architecture
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.
Con Poor ORM
The built-in Waterline is not well designed and is not suitable for production environments. Populating more than 1 level deep is a nightmare, there is no transaction support, new features/bug fixes are not implemented anywhere near a timely manner (the most requested feature 'deep populate' has been lingering in their github issues list for over a year and a half now).