Ramoonus

This plugin adds the Modernizr to your WordPress installation. 
Modernizr is a small JavaScript library that detects the availability of native implementations for next-generation web technologies, i.e. features that stem from the HTML5 and CSS3 specifications. Many of these features are already implemented in at least one major browser (most of them in two or more), and what Modernizr does is, very simply, tell you whether the current browser has this feature natively implemented or not.
For documentation visit http://www.modernizr.com/docs/

Modernizr for WordPress

The 2.8.4 version inserts broken javascript link. I posted a message about this in the support section for the plugin and the author has not responded or fixed the problem. Now, any site that I've added this plugin to can be broken if the user runs an update. 

Instead, if you need Modernizr, insert the following into your header.php file just after <?php wp_head(); ?>:

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/modernizr/2.8.3/modernizr.min.js"></script>

Doesn't work - Plugin Defunct

This plugin adds the Modernizr to your WordPress installation.

whiletrue

duckinformatica

gab.lau

Puts a ribbon on the website if the user browser is older than expected.
Minimum browser versions are customizable in the Settings menu, along with the title and a custom link. 
Now you can set the position and the image of the ribbon. 
This plugin has full support for translation into other languages
For more informations: http://www.duckinformatica.it/prodotti-e-servizi/free-wordpress-plugins/
This plugin uses the Browser detection library built by [Chris Schuld] https://github.com/cbschuld/Browser.php

Browser Update Ribbon

It would be nice to see some guidance on version numbers - is it best practice to always use the lastest version?  If so shouldn't the plug in get that info from somewhere?  If not, then what?  
For now I'll rely on the defaults that are set when you first install it, but maybe the author will stop updating in the future...?  What then?



Works, but...

Puts a ribbon on the website if the user browser is older than expected.

Modernizr for WordPress vs Browser Update Ribbon