Hamed Momeni

this plug-in displays the Browser and Platform of user who commented in your blog. it is capable of determining the version of the borwser.

User Agent Displayer

the User Agent Displayer plugin displays the Browser and the operating system, user used to leave a comment.

Pichel

Displays IP address, operating system, browser type and origin of the visitor by shortcode or as Widget in Sidebar.
Usage
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Place the widget to your Sidebar.
</li>
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You can use the shortcode [about-visitor] to include informations in your posts or pages. 
optional Parameters: 
ip=0 to hide IpAddress 
os=0 to hide Operating System 
browser=0 to hide the Browser 
location=1 to show the location/origin 
Examples: 
List of default informations: [about-visitor] 
List of default informations including location: [about-visitor location=1] 
List only the IP Adress: [about-visitor os=0 browser=0]
</li>
<li>
Without sidebar you can display informations by including in php-code by using then function ‘js_aboutvisitor_display’. 
parameter array: 
ip=>0 to hide IpAddress 
os=>0 to hide Operating System 
browser=>0 to hide the Browser 
location=>1 to show the location/origin 
Examples: 
List of default informations: 
List of default informations including location: 1)); } ?> 
List only the IP Adress: 0;browser=>0)); } ?>
</li>
</ol>

WP Js About Visitor

Displays IP address, operating system, browser type and origin of the visitor by shortcode or as Widget in Sidebar.

User Agent Displayer vs WP Js About Visitor