I assume the objectives here are twofolds: (a) privacy - user is not privy to who is writing what (at least not in a unified way ... ie in one spot ... as the author's name will be on each post, if allowed for by the site owner); and (b) security - user can only post in his/her name.
You can already achieve both of these objectives using two existing plugins.
For (a), you can use Scott Reilly's Custom Admin Post Listing (you have to go to his site, as it is not available in WordPress.org).
For (b), Jordi Canals' Capability Manager plugin is the tool you need.
So, no single plugin to meet both of your objectives. But there are two existing plugins that will produce the same outcome.