Bage

Modal windows are interesting way to include extran information on a page. <a href="http://www.onextrapixel.com/2014/06/25/create-modal-windows-that-can-be-morphed-from-anything-with-jquery-adaptive-modal-js/" rel="nofollow ugc">adaptive-modal.js</a> makes it beautiful. You can use this little plugin which uses the same jQuery plugin to creae modal windows easily in any page or post or even on a widget uisng shortcode.
I have also added another functionality into this plugin, which will let you to embed your modal content into your post a page directly.
<h3>Usage</h3>
Upon activation, the plugin will create a custom post type called ‘Modals’. Where you can add your content, which later you can use it on a modal or embed directly into your page or post.
<ol>
<li>[modal]</li>
<li>[block] </li>
</ol>
<h3>modal</h3>
the ‘modal’ shortcode is to create modal windows.
For now the [modal] shortcode comes with four attributes.
id 
Your modal id. eg: [modal id=2]Click here[/modal]
data 
If your modal only going to have just text, you can directly add the content in the shortcode. eg: [modal data=”This is my modal content”]Click here[/modal]. This shortcode is much useful when you want to add a modal window to a word in a paragrap without braking the paragrap.
<pre><code>note: you cannot use both id and data in the same shortcode
</code></pre>
background 
This is to style the link and the modal window background. Have to specify a valid color. eg: [modal id=2 background=”#DDDDDD”]Click here[/modal]
color 
This attribute is to change the color of the link. eg: [modal id=2 background=”#DDDDDD” color=”#000000″]Click here[/modal]
<h3>block</h3>
The ‘block’ shortcode is to embed your modal content into any page or post. It only has one attribute.
id 
id of the modal post type post.
<pre><code>note: both block and modal shortcodes uses the same Modals custom post type.
</code></pre>

Flexible Modals

Flexible Modal is a very simple plugin to add modal windows to your WordPress content using shortcodes.

themifyme

Themify Popup allows you to display beautifully responsive pop up windows on any page of your website. You can use it to showcase newsletter subscription forms, promotional announcements, or general lightbox content. You can allow popups to show on the entire site, or on certain posts, pages, categories, specific user roles, or even at specific times (so you don’t have to manually disable the popups). It’s fully integrated with the Themify Builder allowing you to design any popup layout on the frontend with the drag & drop interface and live preview.
<h4>Popup Styles:</h4>
<ul>
<li>Auto Close</li>
<li>Classic Center</li>
<li>Fullscreen</li>
<li>Time Delay</li>
<li>Slide-out Bottom</li>
<li>Slide-out Right</li>
<li>WordPress Editor Content</li>
<li>Manual Launch</li>
</ul>
Please visit this page for demos: https://themify.me/popup/.
<h4>Features:</h4>
<ul>
<li>Classic Popup – Show popup with a classic overlay with option to set the popup position</li>
<li>Slide-out – Slide the popup from either top, left, bottom or right edge</li>
<li>Fullscreen – Be extreme! Show the popup fullscreen that covers that entire screen</li>
<li>Schedule Popup – Set the date and time for when the popup with appear. Great for showing promotional popups!</li>
<li>Guests or Admins – Show popups to either guest visitors, logged-in users, or both</li>
<li>Time Delay – Set exactly (in seconds) when the popup will appear</li>
<li>Page Viewed – Show popup when viewer has visited a certain number of pages on the site</li>
<li>Scroll Position – Show popup when viewer scrolls to certain position of the page</li>
<li>Launch Popup Button – Insert a button to launch popup manually (like a lightbox link button)</li>
<li>Popup Dimensions – Enter custom popup dimensions for each popup and set custom overlay color</li>
<li>Animation – Over 40+ animations to choose for opening and closing popup transitions</li>
<li>Show Popup Once – Do not show the same popup to the same visitor for a certain number of days</li>
<li>Auto Close – Close popup automatically after a number of seconds it is opened</li>
<li>Mobile Disable – Options to disable popup on mobile devices (to avoid SEO mobile penalty by Google)</li>
<li>Themify Builder Integration – Design any popup with Themify Builder or the free Builder Lite plugin. It comes with a few sample popup layouts</li>
</ul>
Check out our documentation page here – https://themify.me/docs/popup-documentation

Themify Popup

I have been hunting for a simple, straightforward popup plugin for months. This one works perfectly for my needs; and it does not have conflicts with my themify.me themes.

Very helpful plugin

Turn visitors into subscribers and increase sale conversions! Use Popup to show newsletter forms, promotions, or lightbox content.

Flexible Modals vs Themify Popup