WP Chill

Awaken Solutions Inc.

This plugin allows you to easily mark certain pages with “Permissions” and only users with those permissions will be allowed to see the contents of the page.
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<li>
Page Permissions: This plugin adds a new Permissions taxonomy to your pages. Administrators can create/assign new permissions from the Edit Page screen (you can also use the Quick Edit link). You can add/edit/delete permissions from the Permissions sub-menu under the Pages menu. Pages with no assigned permissions can be seen by everyone.
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User Permissions: Administrators can add/remove permissions from a user using the checkboxes on the Edit User screen. The All Users page has a column that shows the permissions assigned to each user.
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<li>
Restriction Message: If a page has permissions assigned, the content will only be visible to users that have one of those same permissions assigned. Otherwise, the content will be replaced by a generic message or a custom message which can be defined in the plugin settings using the standard WordPress editor (including the ability to add media and formatting).
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Redirect to login: Instead of a restriction message, you can choose to have users get redirected to the login page.
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</ul>

Simple Restrict

Restrict pages based on permissions assigned to pages and granted in user profiles.

KIMoFy

The HTTP Authentication plugin allows you to use existing means of authenticating people to WordPress. This includes Apache’s basic HTTP authentication module, which most servers use.
This plugin works the same way web servers would handle password protection, but in this case, WordPress handles everything.
Ordered list:
<ol>
<li>Password protect a website currently in development.</li>
<li>Secure all admin pages.</li>
<li>Deny access to unauthorized visitors.</li>
</ol>

HTTP Authentication By KIMoFy

Does it's job

HTTP Authentication lets you make a site without letting anyone view it without valid credentials. This can protect the full site or only admin pages.

Simple Restrict vs HTTP Authentication By KIMoFy