The goal of the Sonata Project is to provide a set of high-level features built on top of the Symfony framework, with a strong focus on administration backends. Think of it as a toolkit based on Symfony components to make building sites easy and fun! Famous bundles are already available: Admin Bundle, Block Bundle, Media Bundle, ... and used by other projects like the Symfony CMF. Most bundles are focused on providing CMS and e-commerce solutions, but there are also fairly independent bundles like the Notification Bundle or the Seo Bundle or even libraries like the cache library or the exporter library.
This project is using Symfony Full Stack.