Vitalii

This plugin can to quickly switch user by click. It is comfortable for develop themes and plugins.
After load page, loading neat closed sidebar from right. By click on arrow it show or hide sidebar. Sidebar is 
displaying all registered WordPress users. By click on user is ajax send user ID to back end where switch user. 
After response is JavaScript reload page with registered new user.
<h3>Why using iBryl Switch User?</h3>
<ol>
<li>Quickly switches user by click.</li>
<li>Doesn’t slow down loading.</li>
</ol>

Plugin Name: iBryl Switch User

This plugin can to quickly switch user by click. It is comfortable for develop themes and plugins.

Mitch

WP Maintenance Switch makes it easy to turn on maintenance mode while you are modifying your website.
This light-weight plugin is designed for small operations, such as switching a theme.
If you would like to set up your own custom maintenance page, please <a href="faq/" rel="nofollow ugc">see the FAQ</a>.

WP Maintenance Switch

The button to switch the maintenance mode is so convenient that this extension deserves 5 stars.

Great litlle plugin

A light-weight tool to turn on maintenance mode with just one click.

Plugin Name: iBryl Switch User vs WP Maintenance Switch