Radiant CMS is an open-source content management system that is built using Ruby on Rails. It is designed to be simple and easy to use, making it ideal for small to medium-sized websites.

Some key features of Radiant CMS include:

1. Flexible content management: Radiant allows you to easily create and organize content through its intuitive user interface. You can create pages, articles, and other types of content using a drag-and-drop editor.

2. Customizable templates: Radiant CMS uses a template system that allows you to create and customize the look and feel of your website. You can choose from a variety of pre-built templates or create your own from scratch.

3. Extensibility: Radiant CMS provides a plugin system that allows you to easily add new functionality to your website. There is a wide range of plugins available that can extend the core functionality of Radiant CMS.

4. Multi-site support: Radiant CMS supports the creation of multiple websites within a single installation. This can be useful if you need to manage multiple websites from a single dashboard.

5. SEO-friendly: Radiant CMS comes with built-in support for search engine optimization (SEO). It generates clean and semantic HTML code, which can help improve your website's search engine rankings.

Overall, Radiant CMS is a user-friendly and flexible content management system that is well-suited for small to medium-sized websites. It provides a range of features and options that allow you to easily manage and customize your website's content.