Mirte

If, for example, your clients want to be able to “turn off” their website for a while, so they can work on new 
content or features of their website, but you don’t want them rummaging through the WordPress Settings pages to do so, this plugin might be something for you.
This plugin creates a very simple little widget for your WP Dashboard, from which the website can turned to / out of maintenance mode.
Activating maintenance mode will display a maintenance mode page with explanatory text for your visitors. Logged in users will be able to view the website as they normally would.
The plugin will automatically create a <code>maintenance.php</code> file and add it to your <code>/wp-content/</code> directory. Customize this page to change the appearance and text of the maintenance mode page.
Known bugs 
* Right now, this plugin will not work on certain servers (like Antagonist.nl) because of a permissions issue.

Dashboard Maintenance Mode

Adds a nifty widget to your dashboard from which you can put your website in maintenance mode.

netfett

The maintenance mode only puts the WooCommerce Shop into maintenance mode, but not your entire website. Decide for yourself which text or content should be displayed.
Possible reason for the “Coming soon” mode: 
Your shop is not quite finished yet, but you want to show your visitors that a shop is about to open on your website.
Possible reason for the “maintenance mode”: 
You made an error while configuring or maintaining your products, and you can’t find the error right away. Then switch your shop to “maintenance mode” and take your time to correct the error.
And the best thing is: it’s free! 
Yes, it’s absolutely free. There is no premium version.

Maintenance mode for WooCommerce

Does what it says and is easy

Maintenance mode for the Woocommerce Shop

Dashboard Maintenance Mode vs Maintenance mode for WooCommerce