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.

Amol Nirmala Waman

<a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/" rel="nofollow ugc">Navayan Subscribe</a> allows your visitors to easily and quickly subscribe to your website with double optin process, custom email templates, post/page notifications. Can be used as sidebar widget.
FEATURES
<ul>
<li>Double opt-in Subscribe and UnSubscribe</li>
<li>Default form field – Email</li>
<li>Extended form fields – Name and Custom field</li>
<li>Custom form heading, field labels</li>
<li>Custom Email Templates</li>
<li>Custom Error/Success/Information messages</li>
<li>Option to hide form after success</li>
<li>Send new subscriber notification to admin</li>
<li>Send new post notification to subscribers</li>
<li>Featured image in post notification</li>
<li>Sidebar Widget</li>
<li>Display Subscribe form on Subscribe page</li>
<li>Option to send post content in email</li>
<li>Translate text support</li>
<li>User gets removed if UnSubscribed</li>
<li>Checks whether user is logged in or not</li>
<li>jQuery form validation</li>
<li>HTML5 Placeholder</li>
<li>HTML5 Validation with jQuery fallback</li>
<li>Displays various users count</li>
<li>Show Subscribers count – Optional</li>
<li>Works with Custom Post Types too</li>
<li>Restricts specific IPs, Domains, Emails with custom messages</li>
<li>Active theme CSS for email templates</li>
</ul>
Take a look at <a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/" rel="nofollow ugc">Screenshots</a>
Links
<ul>
<li><a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/" rel="nofollow ugc">Plugin’s Homepage</a></li>
<li><a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/#comments" rel="nofollow ugc">FAQs & Discussion</a></li>
<li><a href="http://blog.navayan.com/wordpress/" rel="nofollow ugc">Similar Topics</a></li>
<li><a href="http://blog.navayan.com/navayan-csv-export-easiest-way-to-export-all-wordpress-table-data-to-csv-format/" rel="nofollow ugc">Navayan CSV Export</a></li>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=amolnw2778@gmail.com&item_name=NavayanSubscribe" rel="nofollow ugc">Donate (Dhammadana)</a></li>
<li><a href="http://www.navayan.com/donate.php" rel="nofollow ugc">More Donate Options</a></li>
</ul>
<h3>Usage</h3>
<ol>
<li>Activate the plugin</li>
<li>Go to Dashboard -> Tools -> Navayan Subscribe</li>
<li>Customize the form settings and email templates as you want</li>
<li>Go to ‘Appearance -> Widgets’, drag and drop ‘Navayan Subscribe’ widget in one of your sidebars.</li>
</ol>
If you feel this plugin saved your efforts, it would be great if you Rate it!
Links
<ul>
<li><a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/" rel="nofollow ugc">Plugin’s Homepage</a></li>
<li><a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/" rel="nofollow ugc">Screenshots</a></li>
<li><a href="http://blog.navayan.com/navayan-subscribe-easy-way-to-subscribe-wordpress-website-or-blog/#comments" rel="nofollow ugc">FAQs & Discussion</a></li>
<li><a href="http://blog.navayan.com/wordpress/" rel="nofollow ugc">Similar Topics</a></li>
<li><a href="http://blog.navayan.com/navayan-csv-export-easiest-way-to-export-all-wordpress-table-data-to-csv-format/" rel="nofollow ugc">Export WP to CSV</a></li>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=amolnw2778@gmail.com&item_name=NavayanSubscribe" rel="nofollow ugc">Donate (Dhammadana)</a></li>
<li><a href="http://www.navayan.com/donate.php" rel="nofollow ugc">More Donate Options</a></li>
</ul>
<h3>Donate</h3>
We call ‘Donation’ as ‘Dhammadana’. It help us to contribute more to open source community. 
<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=amolnw2778@gmail.com&item_name=NavayanSubscribe" rel="nofollow ugc">Donate ie. Dhammadana</a>

Navayan Subscribe

Allows visitors to easily and quickly subscribe to your website with double optin, email templates, notifications, block spam.

Logical Captcha vs Navayan Subscribe