I'm Didier from LocomotiveCMS.
LocomotiveCMS is a little bit different from the other CMS, in a sense, we offer a tool named Wagon to manage your site locally without having to install mongodb, rails and some other components. Another huge benefit is that you can write your templates in HAML and your CSS in SASS/ SCSS or Less (we embedded Compass as well) and with our preferred texts editor (editing a whole site in a browser is a nightmare). That's a nice eco-system in order to be super efficient when it comes to develop a LocomotiveCMS site.
Once you're done with your local work, you can deploy your site to a remote LocomotiveCMS engine in a similar way you push your application to Heroku. Actually, pushing a site will create the back-office for the final end user.
I suggest you to read that page. http://doc.locomotivecms.com/guides/get-started/requirements and this one too http://www.locomotivecms.com/tour
Our message is still not clear on our official website but believe me, we are working to make it better.
Hope it will help you !
Didier