DCoda

This plugin is only supported on PHP 5.2 or greater.
 
MembersBlog easily allows you to lock down your blog to members only. 
Unauthenticated visitors who try to view the blog content will be forced to the login page , or presented with an browser login prompt if they try to view the feed.
When the blog and feed are locked down to subscribe to a feed using a feed reader a username and password must be supplied in the url:
<pre><code>http://{username}:{password}@{feed url}
</code></pre>

If you are having trouble and cannot find the answers in the <a href="http://membersblog.dcoda.co.uk/help/faq/" rel="nofollow ugc">FAQ</a> you can post your support questions to the <a href="https://wordpress.org/tags/members-blog" rel="ugc">WordPress Support Forum</a>
If you find MembersBlog useful please rate it at <a href="https://wordpress.org/extend/plugins/members-blog/" rel="ugc">wordpress.org</a> and please consider making a <a href="http://membersblog.dcoda.co.uk/donate/" rel="nofollow ugc">donation</a> to help us set aside more hours to maintain MembersBlog
MembersBlog is written by <a href='http://dcoda.co.uk' rel="nofollow ugc">dcoda</a>
You can check out our other plugins <a href="https://profiles.wordpress.org/users/dcoda/" rel="nofollow ugc">here</a>
If you require a custom plugin you can contact us <a href="http://dcoda.co.uk/contact/" rel="nofollow ugc">here</a> and maybe we could write it for you.
<h3>Copyright</h3>
(c) Copyright DCoda Limited, 2007 -, All Rights Reserved.
This code is released under the GPL license version 2, available here:
<a href="http://www.gnu.org/licenses/gpl.txt" rel="nofollow ugc">http://www.gnu.org/licenses/gpl.txt</a>
There are so many possibly configurations of installation the plugin can be installed on we limit testing to a PHP 5.2+ Linux platform running the latest version of WordPress at the time of release but it is released WITHOUT ANY WARRANTY; 
 without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

MembersBlog

Lock down all your posts and pages so only members can access them

Buddypress pages are public by default. This plugin allows you to restrict not logged-in users from accessing these pages.
If an anonymous user tries to access these pages, they will be redirected either to the login page, or to the homepage, or even to a custom page.
The plugin also allows to display on these pages a template with a message to log in instead of directly redirecting them elsewhere.
<h3>Features</h3>
<ul>
<li>Very easy to use, you only have to choose which pages want to retrict to anonymous users (not logged-in users).</li>
<li>Small and lightweight plugin (around 10-15kb).</li>
<li>No CSS, no scripts. No requests to static files.</li>
<li>Fully translated into Spanish.</li>
</ul>
<h3>Support</h3>
Need help? Any bugs to report? Any suggestions? Please contact me.
You can help me too either by rating this plugin or by making a donation.

Buddyfence

This plugin allows you to restrict not logged-in users from accessing BuddyPress pages

MembersBlog vs Buddyfence