Grav is a fresh flat-file database which is easy to install. It uses a number of Symfony components and is very fast to get started with.
Grav is a newcomer to the PHP CMS scene. It is a flat-file CMS, which means content is stored into files - not a database (like MySQL, PostgreSQL, MongoDB, SQLite...). This simplifies installation and makes moving the installation easy.
Grav uses Symfony components and also the familiar Twig templating engine. This makes it easy to get started with Grav and then porting your content and templates if (and when) your needs grow beyond what the flat-file approach allows you.
Grav is a new project which means the code is clean and the UI is contemporary. The system should probably not be stretched too far, but it's great for static content sites and quick prototyping.