You won't be able to build Clarity on Word Press. It's a content management system so while powerful is extremely limited compared to what you could do with Ruby or any other software language. But as someone else identified here you're comparing apples to oranges. Word press will give you a website quickly and you can make some tweaks and changes within the limitations of WordPress and it's plugins. Ruby on rails is entirely different - you can build whatever you want. Although it will take longer and cost more, you'll be able to create a web application as opposed to just a website. Hope that helps!