tidingsco

This plugin lets you publish newsletters from your Tidings account to WordPress with the click of a button.
Install, activate, and go to the Tidings section of the Settings menu to configure the plugin.
Simply paste your Tidings Account Key, confirm the default category and author for each post, and you’re off to the races!
If desired, you can tailor the HTML tags used by each newsletter attribute. Styling is inherited (and customizable) via your theme’s CSS file.

Tidings

Publish your Tidings email newsletters to your Wordpress blog or website.

EverPress

Xaver

Mailster Newsletter Plugin

Integrates Mailster Newsletter Plugin with Gravity Forms to subscribe users with a Gravity Form. 
Requires the Mailster Newsletter plugin and the Gravity Forms plugin
<blockquote>
This Plugin requires <a href="https://mailster.co/?utm_campaign=wporg&utm_source=wordpress.org&utm_medium=readme&utm_term=Gravity+Forms" rel="nofollow ugc">Mailster Newsletter Plugin for WordPress</a>
</blockquote>

Mailster Gravity Forms

Integrates Mailster Newsletter Plugin with Gravity Forms to subscribe users with a Gravity Form.

Tidings vs Mailster Gravity Forms