Yellow is for people who make websites. It's a flat-file content management system. Everything is made of files and folders. You can create web pages, blogs, wikis. There's support for Dropbox, Markdown, dynamic and static pages.
Lacks available extensions or plugins, and extending functionality requires custom programming.
Management of content and data is relatively straight forward, but there may be a bit of a learning curve. Some programming experience may be required.
Lacks an active community, and there is no or minimal support provided. Lacks proper documentation.