Chris Lanphear

A very simple plugin to disable the Block Editor (formerly known as Gutenberg) and restore the classic WordPress editing experience. 
There are no settings. If Guten-bye is active, the Block Editor will be disabled for all registered post types and the original 
“Classic” editor will be used in its place.

Gutenbye

A very simple plugin to disable the Block Editor (formerly known as Gutenberg) and restore the classic WordPress editing experience.

mch0lic

Recently upgraded to WordPress 3.8+ and not yet ready for the visual change? WP Admin Classic plugin simply disables new admin theme and reenables the prior 3.8 looks to your admin panel. Please, note that there is still some unsolved issues (see “Issue list), so if you have ideas how to solve it just shout!
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Issue list:
<ol>
<li>
RTL Languages are not yet supported!!!
</li>
<li>
Post edit form turns blue (as a result for fixing http://1?ver=3.8 issue)
</li>
<li>
Admin bar is not displayed properly on front-end with standard Twenty Thirteen, Twenty Fourteen (updated themes).
</li>
</ol>
Notes:
<ol>
<li>Dashboard widgets are now 100% wide. CSS fix by Robert Heller (Single column only!).</li>
</ol>
Please, report any other CSS/JS issues and suggestions how to fix them <a href="https://wordpress.org/support/plugin/wp-admin-classic" rel="ugc">here</a> or <a href="http://mindomobile.com/contact-us/" rel="nofollow ugc">here</a>. Your help much appreatiated.
ENJOY!

wp-admin classic

Classic WordPress Admin theme (prior 3.8 style).

Gutenbye vs wp-admin classic