What? A hosted content management system that makes it easy to build database-driven sites with complete design and data customization.
Why? More capable than Wordpress, if you need more than a blog; much less painful than Drupal.
Who? Web designers and others who can deal with HTML and CSS and want robust back-end capabilities without having to write server code.
How? It's a hosted service, so you do everything through the browser. Internally, it uses Ruby on Rails.
Diff? Easy support for structured content. Ability to completely customize the design and create databases without back-end programming.
Webvanta