Squarespace is a slick CMS, that is hosted as a Service (by the company).
It’s made with a design focus and can be used for portfolio building, brand strategies etc.
It’s a design-first philosophy (design has prio, functionality comes second)
Unlike WordPress, it cannot be extended with PHP
you can add custom CSS and JavaScript
Its API is very limited
My use-case for it is creating a beautiful design-first front page for my think tank space.