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.

DRegister (which stands for Dr. Register) is a clean and easy plugin that allows you to :
<ul>
<li> Force your user to provide First and Last name upon registration</li>
<li> Create custom fields and specify if they have to be, alphanumeric, numeric only or multi-choice (radio) , plus if they are required to complete registration.</li>
<li> Clean use, no MySQL tables are created. User data is stored as WP User Meta and you can keep track of meta keys for further use.</li>
<li> Custom fields are available for editing on each user profile page.</li>
<li> Uses Mootools for smooth AJAX administration.</li>
<li> Working fine on WP 2.7.1.</li>
</ul>

Languages included: English, Italian, Hungarian,Spanish
Want to translate this plugin? Contact me at webmaster [at] juzaam.com
Translation credits:
<ul>
<li>Hungarian: J?nos Cs?rdi-Braunstein <a href="http://blogocska.org/" rel="nofollow ugc">http://blogocska.org/</a></li>
<li>Spanish: Alejandro Urrutia <a href="http:/www.theindependentproject.com" rel="nofollow ugc">http:/www.theindependentproject.com</a></li>
</ul>
<h3>LOCALIZATION</h3>
<ul>
<li>Place your language file in the plugin folder directory and name it “dregister-{language}.mo” replacing {language} with your language value from wp-config.php</li>
</ul>

DRegister

Enhance your Registration Page. Require First Name, Last Name. Add custom fields. Require custom fields.

Logical Captcha vs DRegister