JamesClarke

Private URL is a plugin for sharing private posts through a special private url which is accessible without requiring readers to register or enter a password. Private URLs have a structure similar to <code>/private/293/df8eb1583b052b59e2cafc4327214d0/</code>.
<h3>Usage</h3>
When you edit a private post a new options panel will become available called Private URL. This provides the private url and a means for changing the salt for the post. The url is a publicly accessible version of the private post and typically of the form: <code>/private/293/df8eb1583b052b59e2cafc4327214d0/</code>
<h3>What is the salt?</h3>
The salt is responsible to generating the private url for each post. It is similar to a passphrase. By default all posts use the salt provided in the settings page for Private URL. However, you can specify a post specific salt using the Private URL options panel while editing a post.
Modifying the salt for a post will cause it to have a new private url and the post’s old private url will no longer function. This can be used as a means to expire an old private url for the post. Changing the default salt in the options menu will cause all posts without their own salt to have new private urls.

Private URL

Allows private posts to be shared through a special private url.

ellbristow

Force all posts by users without Editor or higher role to be private.
This plugin allows you to give your post writers the ability to create and publish posts on your site that are only visible to 
the author, and to editors/admins, by forcing all their posts to be private.
Features:
<ul>
<li>Anyone who does not have the ‘edit_private_posts’ capability can only post private posts</li>
<li>Limit all posts, or only newly added posts</li>
<li>(Optional) Also force a post to have a specific category when posted</li>
<li>Editors, admins and Super admins (who do have the ‘edit_private_posts’) can see all posts, and switch them from private to public if required.</li>
<li>No Configuration!</li>
<li>Just Activate!</li>
</ul>
This is my first publicly released plugin… so I hope you like it. Let me know if you find any bugs!

ForcePrivate

Force all posts by users without Editor or higher role to be private

Private URL vs ForcePrivate