With WebConstruct you can set your website/application offline. When a visitor visits you website he gets a customizable under construction page. While you as admin can still visit all the pages on your website and work on them.
This script is very easy to implement. The only thing you need to do is include one line of code at the first line of your index.php file. To configurate the message to show you can use the password protected admin panel.
The under custruction page is loaded from a template so you can create your own under construction page that fits with the theme of your site.
Themable under construction page
Password protected admin panel to change configuration
3 example themes included
Very easy to use
You can also use this for WordPress and other popular CMS ’s. To see how to install it under WordPress you can take a look at this How to install under WordPress video.