Mindvalley

Outputs $_POST or $_GET variable values using shortcodes.
Super duper uberly useful on tracking scripts on eCommerce thank you pages.
Example:
<ul>
<li>$_POST[’email’] > [post_var name=”email”]</li>
<li>$_GET[‘txn_id’] > [get_var name=”txn_id”]</li>
</ul>
For Array values :
<ul>
<li>$_POST[‘user’][’email’] > [post_var] name=”user[email]” [/post_var]</li>
<li>$_GET[‘user’][‘first_name’] > [get_var] name=”user[first_name]” [/get_var]</li>
<li>$_GET[‘user’][‘address’][‘line1’] > [get_var] name=”user[address][line1]” [/get_var]</li>
</ul>
Note: Remember to wrap the name attribute in double quotes (“).

Mindvalley Post & Get Variables

Lets you output a POST or GET variable in the page via shortcode.

Alex Prokopenko / JustCoded

This plugin allow you to create simple text variables (single/multi-line) to use them in your theme templates after that. 
Once you added at least one variable, a new page called Theme Variables will appear under the Appearance menu. 
You can move all your text data (like copyright text, phone numbers, address etc.) to variables. 
So if the final client wants to change this text, he can do this easily as admin without editing the template.
This project is also available on github.com: 
https://github.com/aprokopenko/justvariables.
You can post issues, bugs and your suggestion in Issues tracker there.

Just Variables

This plugin allow you to create simple text variables (single/multi-line) to use them in your theme templates after that.

Mindvalley Post & Get Variables vs Just Variables