The Good Suite is a php framework that intends to make it easier to make better websites and web applications.
The Good Suite is written in php, so the one requirement is for you to be working in php. However, the framework also has components that help you deal with html, css and javascript, so it does not limit itself to just php.
The Good Suite is a framework in the sense that if you choose to use all of it, it intends to provide the entire environment for you to create your website or web application in. At the same time, one might also describe it as a set of libraries, as the idea is that you only use those parts of the framework that you like and you don't have anything that then ties you to the other modules.
The intention of The Good Suite is to make it easier to make your website by having you spend less energy on anything that's not the specific content of your website. This means it aims to take care of common tasks such as a log-in system in for you, as well as usage of other technologies such as the database access.
The aim to let you create better websites is based on letting the framework take the care of the security of your website wherever possible, letting you write websites that are not dependend on a specific underlying technology and helping you keep different aspects of your website seperated.