Bolt CMS is a lightweight CMS built with the Silex Microframework. It is well built and a great alternative for developers looking for a modern PHP system to replace WordPress, for example.
Bolt CMS is built from the beginning on the on the Silex microframework. Silex is a lightweight web framework built with Symfony Components. The framework does not enforce specific conventions for you, but gives you a quick way to get started with small applications.
Bolt is a good example of product management as they have intentionally left features outside of the Major release, 3.0: Some things that will not be in Bolt 3.0. This makes a Bolt a great alternative to WordPress, for smallish sites that focus on content and require great usability.
Bolt is not a very known brand compared to some of the competition and limits the availability of possible integrators and agencies. The modern structure makes it fast to learn and the Bolt Extension Store provides many commonly used bits and pieces.