You can search for multi-user blogging platform or similar term.

If you want something free you can try the multi-user from mu.wordpress.org if you want something paid, I think typepad has something similar.

As far as I know, you don't need Wordpress MU to accomplish having several authors posting to the same blog - in the standard version, just check off the "may submit drafts for review" box in the options. I've never used that particular feature, but it sounds like what you are looking for.