Digits let your user signup on your website simply with their mobile number. No more checking emails.
Demo: https://codecanyon.net/item/digits-wordpress-mobile-number-signup-and-login/19801105
What is flutter? Flutter UI Kit Flutter is an open-source mobile application development SDK created by Google.
Demo: https://codecanyon.net/item/flutter-login-and-signup-ui-responsive-template-beautiful-design/32952330
MailChimper PRO is a WordPress MailChimp Form Plugin, that support MailChimp along with many more other providers.
Demo: https://codecanyon.net/item/mailchimper-pro-wordpress-mailchimp-signup-form-plugin/7644126
This script is a simple php script that allow your clients to register free email for themselves without them having access to the cpanel.
Demo: https://codecanyon.net/item/cpanel-email-signup-and-login/3753815