kepon

The widget only shows if AdBlock (or another) is not installed. Message can be customized within widget page and download link is related to the visitor’s browser.

Adblock invite (Yes adblock)

Detects if the visitor have AdBlock (or another) plugin/extension installed and if not, gives URL to download it

freemp

A lightweight WordPress plugin providing the <code>[recaptcha-js-alert]</code> shortcode which may be used to display a notification text box if JavaScript required by reCAPTCHA is being blocked.
Next to the notification message text and the delay allowing to load the reCAPTCHA JavaScript code, the plugin offers configuration of background and foreground color, as well as the font size. Further customization can be achieved by means of custom CSS snippets.
The shortcode allows its configuration being overridden by the following parameters:
<ul>
<li><code>message</code>: The notification message text</li>
<li><code>style</code>: Custom CSS for displaying the message text</li>
<li><code>delay</code>: The delay (in milliseconds) allowing the reCAPTCHA JavaScript code to load</li>
</ul>

ReCaptcha JS Alert

ReCaptcha JS Alert provides the [recaptcha-js-alert] shortcode, which (if necessary) informs visitors of your website that a form requires JavaScript  …

Adblock invite (Yes adblock) vs ReCaptcha JS Alert