Piranha CMS is very simple, light weight, extensible open source framework. This is a framework for keeping the content in mind. You will be up and running in no time. The framework is built on Microsoft patterns and easily adopts your workflow whether you’re using ASP.NET MVC or web pages. By using the simplicity of CMS, we can easily inject this framework in our existing projects. This CMS comes with two packages. This CMS provides the user authentication, pages and page type out of box. There are many more features this framework is offering. You can read complete details here. https://piranhacms.org/features
I found their documentation very helpful and simple https://piranhacms.org/docs/introduction. They explained every entity in detail. Building a customized app in top of this very easy and we can use CMS properties in our custom development by implementing few attributes.
Here is the url of Piranha home page.
https://piranhacms.org/