Tammy Hart

This plugin adds a page to the admin under Users that includes a form for users to send email invitations to their friends to register at your site. You can also add the form to the front end of your site with the <code>invite_friends()</code> template tag or the <code>[invite_friends]</code> shortcode.
IMPORTANT: This plugin will not allow invited friends to register unless you have registration turned on.
<h4>Features</h4>
<ul>
<li>Invite multiple friends at one time</li>
<li>Customize the email subject and message that is sent</li>
<li>Customize the URL to redirect a user to after they register</li>
<li>Store successful registered users in the inviter’s user meta data</li>
<li>Store the inviter in the new user’s meta data</li>
</ul>

Invite Friends to Register

Use this plugin to allow users to invite their friends to register on your site.

DigitalME

This plugin adds a simple WordPress button linking to your Discord server. 
You can set your Discord invite URL once in the Settings page, and use the shortcode anywhere in posts, pages, or blocks.
Features: 
* Shortcode [digitalme_discord_button] to place the button anywhere 
* Global settings page for Discord URL under Settings → Discord Button 
* Fixed text (“Join our Discord!”) and styling 
* Lightweight and fully WP.org compliant

DigitalME Join Button for Discord

A simple shortcode and settings page to display a fixed 'Join our Discord!' button.

Invite Friends to Register vs DigitalME Join Button for Discord