Justin Busa

This plugin allows you to hide the WordPress admin, login and signup pages from all users except those with a specific capability. Unauthorized users will be redirected via a 301 redirect to your site’s homepage or a URL that you specify in the settings.
This plugin is useful if you want to allow signups for your site but only want users with a certain capability (e.g. edit_others_pages for editor and administrator) to be able to access the admin area. This helps to ensure that malicious users can’t access something that you didn’t intend for them to access.
You are also given the option to redirect the WordPress login and signup pages to your own custom pages. Redirecting those pages in addition to the admin can also help secure your site from someone trying to attack those URLs.
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Hidden WP Admin

Hide the WordPress admin, login and signup pages from all users except those you allow.

itthinx

The plugin protects a site so that only members can access its pages.
Suitable for site lockdowns, private sites and sites that are under construction.
It allows to redirect visitors to a particular page or to the WordPress login.
Members who are logged in have access to the site. 
Members must belong to the site’s Registered group, or to a particular group as determined specifically for the site.
The plugin is an extension to <a href="https://wordpress.org/plugins/groups/" rel="ugc">Groups</a> which is required.
The redirection settings can be adjusted in Settings > Groups Blog Protect :
Redirection options can be set for the blog – or for each blog in a multisite setup:
<ul>
<li>no redirection</li>
<li>redirect to a specific post, note that with this option the blog is shown to the visitor but only that page can be visited</li>
<li>redirect to the WordPress login</li>
</ul>
The redirect status code can be selected among:
<ul>
<li>Moved Permanently (301)</li>
<li>Found (302)</li>
<li>See other (303)</li>
<li>Temporary Redirect (307)</li>
</ul>
Site administrators can determine which group is used to protect the site:
<ul>
<li>By default, users must belong to the Registered group to be able to access the site, so any registered user who is logged in will have access.</li>
<li>The constant <code>GROUPS_BLOG_PROTECT_GROUP</code> can be set in <code>wp-config.php</code> to indicate the name of the group to which users must belong to be able to access the site.</li>
<li>For multisites, the <code>GROUPS_BLOG_PROTECT_GROUP_n</code> constant can be used to indicate the name of the group required to access a particular site, where <code>n</code> is the blog ID of the site.</li>
</ul>

Groups Blog Protect

Protect access to blogs via group memberships powered by Groups.

Hidden WP Admin vs Groups Blog Protect