Mahfuzar Rahman

The MailChimp plugin allows you to quickly and easily add a signup form for your MailChimp list as a widget on your WordPress 2.8 or higher site.
Not sure what <a href="http://www.mailchimp.com/features/full_list/" rel="nofollow ugc">MailChimp</a> is or if it will be helpful? Signup up for a <a href="http://www.mailchimp.com/signup/" rel="nofollow ugc">FREE Trial Account</a> and see for yourself!
After Installation, the setup page will guide you through entering API information, selecting your List and then add the Widget to your site. The time from starting installation to have the form on your site should be less than 5 minutes – absolutely everything can be done via the WordPress Setting GUI – no file editing at all!
<h3>Developer Mode</h3>
You can enable “Devleoper Mode” by adding the following line to your <code>wp-config.php</code> file just above the “That’s all, stope editing!” line.
<pre><code>define('MAILCHIMP_DEV_MODE', true);
</code></pre>
This will enable the MailChimp List Subscribe plugin to operate without the need to connect an external MailChimp Account, and will provide a 
subscription form widget that will not actually submit anywhere.
This will allow you to style and configure the widget in non-production environments that are not publicly accessible.
For more Developer Mode customization options see the following article:
http://connect.mailchimp.com/how-to/how-to-article-configuring-developer-mode-for-the-list-subscribe-wordpress-plugin

Easy Mailchimp Optin Form

The MailChimp plugin allows you to quickly and easily add a signup form for your MailChimp list as a widget on your WordPress 2.8 or higher site.

Concerted Action

A free WordPress plugin for the <a href="https://actionnetwork.org" rel="nofollow ugc">Action Network</a> online organizing tools maintained by <a href="http://concertedaction.consulting/" rel="nofollow ugc">Concerted Action</a>.
Features:
<ul>
<li>Create a WordPress shortcode or widget from any Action Network embed code.</li>
<li>Manage your saved embed codes using the WordPress backend. Supports sorting by title, type and last modified date, and provides a search function.</li>
<li>Modify Action Network’s default “thank you for your support” and “help us by using sharing tools” messages, and control which sharing options (social, email & embed codes) are displayed, using shortcode options or widget controls.</li>
<li>Use <code>[actionnetwork_list]</code> shortcode or Action Network List widget to show a list of current actions.</li>
<li>Use <code>[actionnetwork_calendar]</code> shortcode or Action Network Calendar widget to show a list of upcoming events. Optionally outputs upcoming events in JSON. Development of this feature was supported by <a href="http://www.thepeopleslobbyusa.org/" rel="nofollow ugc">The People’s Lobby</a> – if you like it, please consider <a href="https://actionnetwork.org/fundraising/donate-to-the-peoples-lobby" rel="nofollow ugc">making a donation to them</a>.</li>
<li>If you are an <a href="https://actionnetwork.org/partnerships" rel="nofollow ugc">Action Network Partner</a>, use your API key to sync all of your actions from Action Network to WordPress.</li>
<li>Create signup widgets which allow visitors to your site to sign up for your email list without using Action Network javascript embeds. This allows you to place a signup form on every page (for example in the sidebar), and still load Action Network embed codes for actions on particular pages (since Action Network’s scripts will only load one embed code per page). This feature does require the API key, so you have to be an <a href="https://actionnetwork.org/partnerships" rel="nofollow ugc">Action Network Partner</a> to use it.</li>
</ul>
Detailed specs for shortcode attributes, widget options, etc. are available on the Help menu for the Action Network page on the backend.

Action Network

Provides Action Network (actionnetwork.org) action embed codes as shortcodes and a calendar and signup widget

Easy Mailchimp Optin Form vs Action Network