Logical Captcha takes advantage of the TextCaptcha.com service, which provides logic-based textual questions instead of distorted images or audio to validate that the entity registering is a real live human being, and not a spam bot. It will provide protection against false registrations and the dreaded spam comments, etc.
An example of such a question might be:
Question: 
Out of a truck, a lion, the color purple, and the number forty-two, which has a door?
Answer: 
truck
Textual logic-based captchas mean that your registration process will be accessible to everyone, including visually/hearing impaired visitors who use access technology to surf the web. It requires a free API key from <a href="http://TextCaptcha.com" rel="nofollow ugc">TextCaptcha.com</a>
This plugin was developed by Josh de Lioncourt of <a href="http://maccessibility.net" rel="nofollow ugc">the Mac-cessibility Network</a>, a site dedicated to blind and visually impaired users of the Mac OS X operating system, the iPhone OS, and other Apple Inc. products and services. Josh de Lioncourt, the Mac-cessibility Network, and related sites are not in anyway affiliated with TextCaptcha.com

Logical Captcha

Integrates a logic captcha to verify that the registrant is a human and not a spam bot instead of using distorted images or audio.

sunnyverma1984

Increase user registration on blog by making post or page available only for registered user. 
This plugin allows to make post, page or partial content visible to registered users only. You can hide partial content using shortcode <code>[RegUserOnly][/RegUserOnly]</code>. Or you can hide complete post or page by selecting Visibility to <code>Registered Users</code> in post/page editor.
<h4>Plugin Features</h4>
<ul>
<li>Easy installation and integration</li>
<li>Custom tinymce shortcode button</li>
<li>Cross Browser capability</li>
<li>Translation ready</li>
</ul>

Only for Registered Users

Make post, page or partial content visible to registered users only

Logical Captcha vs Only for Registered Users