elrata_

NOTE: I’m looking for a new maintainer. Please reach out to 
rodrigo@sdfg.com.ar if you are interested.
NOTE: I don’t have wordpress 5 installations to try this and plan to stop 
updating it. If this is a big issue for you, please let me know so I can 
consider to continue doing it. Also, let me know if you are willing to help with testing :).
This is a small modification of the wp-recaptcha plugin to make it work with 
BuddyPress. Currently uses recaptcha v2.
You only need this plugin if you use Buddypress with wordpress and want a 
recaptcha at the registration page.
It is always rebased on top of wp-recaptcha. See 
https://github.com/rata/wp-recaptcha-bp for more info
What is reCAPTCHA?
reCAPTCHA is a free CAPTCHA service that protects your site against spam, malicious registrations and other forms of attacks where computers try to disguise themselves as a human; a CAPTCHA is a Completely Automated Public Turing test to tell Computers and Human Apart. reCAPTCHA comes in the form of a widget that you can easily add to your blog, forum, registration form, etc.
In addition to protecting your site, reCAPTCHA also helps us digitize old books and newspapers, transcribe street numbers and solve hard AI problems. <a href="http://www.google.com/recaptcha" rel="nofollow ugc">Learn how reCAPTCHA works</a> and join our <a href="https://groups.google.com/forum/#!forum/recaptcha" rel="nofollow ugc">forum</a>.
<h3>Requirements</h3>
<ul>
<li>You need the reCAPTCHA keys <a href="https://www.google.com/recaptcha/admin#whyrecaptcha" rel="nofollow ugc">here</a>.</li>
<li>Your theme must have a <code>do_action('comment_form', $post->ID);</code> call right before the end of your form (Right before the closing form tag). Most themes do.</li>
</ul>

WP-reCAPTCHA-bp

Integrates reCAPTCHA anti-spam methods with WordPress sites using BuddyPress plugin, including comment and registration spam protection.

Olaf Lederer

This free contact form plugin is used to create accessible contact forms with advanced spam protection (honeypot, cookie and optionally Cloudflare Turnstile or hCaptcha). In contrary to most other form plugins, there is no form-builder included.
<h4>Features</h4>
<ul>
<li>The generated form is accessible and works even when the visitor has disabled Javascript</li>
<li>Accessible form field validation</li>
<li>Protect your forms against spam bots using a honeypot and cookies</li>
<li>Track successfully submitted forms in Google Analytics and/or Clicky</li>
<li>Create multiple contact forms via an easy to use interface and add the form via the block editor or using a shortcode</li>
<li>Collect form submissions for all your forms or the forms you choose</li>
<li>Get insights which spam protection feature works the best for your form. A simple log file keeps track about the different spam attempts</li>
<li>Multiple responder emails, send a HTML formatted mail in response to the form submission</li>
<li>Works with the default wp_mail() function (use it together with the <a href="https://wordpress.org/plugins/simple-smtp-by-maileroo/" rel="ugc">Maileroo</a> plugin to send emails via SMTP)</li>
<li>Optional: Protect your forms by blocking specific countries which are not relevant for your website or business</li>
<li>Optional: Protect your contact form with the plugin <a href="https://wordpress.org/plugins/honeypot/" rel="ugc">WP Armour – Honeypot Anti Spam</a></li>
<li>Optional: Email address verification with the verification API from <a href="https://maileroo.com/?r=acfplugin" rel="nofollow ugc">Maileroo</a></li>
<li>Optional: Form fields for Company name, phone number, website and an accept terms checkbox</li>
<li>Optional: Redirect the visitor after a succesful form submission to a “Thank you” page</li>
<li>Optional: Use the plugin’s CSS style-sheet for your forms</li>
<li>Optional: Protect your forms with Cloudflare Turnstile or hCaptcha</li>
<li>Optional: For additional spam protection, you can add a simple and accessible challenge to your form.</li>
</ul>
The plugin is built to keep stuff simple. If you need a complex web form or if you need a form builder, please use one of the form plugins you can find in the WordPress repository. To use the “Block countries” feature we use the IP to Country API from Country.is. They offer a free service and you don’t need an API key.

Ajax Contact Form

An easy to use contact form plugin with multiple inbuilt features to prevent contact form spam.

WP-reCAPTCHA-bp vs Ajax Contact Form