Sabaoh

This plugin will add some reCAPTCHA widget to login form, comment form, and user registration form. With this plugin, sites owners can avoid spam comment, user registration, and biting password.
Mighty CAPTCHA uses a Google reCAPTCHA technology. To work, API key pair, issued Google, is necessary.
For more information about key pair, please refer https://www.google.com/recaptcha/intro/index.html .
You can choose which form will be with reCAPTCHA widget or not. For login form and user registration form, a normal size widget is too wide. So you can choose compact widget. (but I do not like it.)
Below is characteristic of new Google reCAPTCHA.
<ul>
<li>Easy for ordinary users. They only must check the “I’m not a robot”.</li>
<li>When Google reCAPTCHA recognized an access was smell fishy, image authentication screen would appear.</li>
<li>New image authentication screen is without deformed letters, with photo images instead of them.</li>
<li>Photo images authentication is for example “choose all photos of a cat”. Easy to human and hard to robot.</li>
<li>It’s easy to use with smart phone or tablet.</li>
</ul>
Why don’t you usher it into your site!

Mighty CAPTCHA

Mighty-CAPTCHA add an authentication with Google reCAPTCHA technology to login, comment, and register form, with API keys which delivered by Google.

Ipstenu (Mika Epstein)

JohnnyWhite2007

Spam is one thing, but trolls and sock puppets are another. Sometimes people just decide they’re going to be jerks and create multiple accounts with which to harass your honest users. This plugin helps you fight back by logging the IP address used at the time of creation.
Log into your WP install as an Admin and you can look at their profile or the users table to see what it is. For security purposes a user’s own IP is not displayed to them when they look at their own profile.
<ul>
<li><a href="https://ko-fi.com/A236CEN/" rel="nofollow ugc">Donate</a></li>
</ul>
<h3>Privacy Notes</h3>
This plugin adds additional data to a new user’s <code>wp_usermeta</code> data under the <code>signup_ip</code> key. This data is directly tied to the user account, and is only editable via the database. Should a user account be deleted from the site, the data will be automatically deleted.
No external data is transmitted, it all stays on your install.

Register IPs

Does exactly waht it says

When a new user registers, their IP address is logged. Supports multisite and single site!

Mighty CAPTCHA vs Register IPs