vinmatrix

Sometimes we need to have more fileds for WordPress administrator,Lets us take an example, we have only 
one admin mail setting in wordpress, and if we need more than one then we need to have an interface to maintain 
other email ids. Like this we can maintain N number of custom fileds dynamically through this WP Admin Custom files plugin.

WP Admin Custom Fields

Allows to maintain N number of Custom fields dynamically for site administrator.

itcoderr

This plugin gives you a way to choose what widgets display on each page/post of your website. The plugin’s custom sidebars provides a way, using that you can display custom widget configurations on any page, post, post type, or archive page.
Features
<ul>
<li>Unlimited custom widget configurations</li>
<li>Custom widget for individual post, page etc..</li>
<li>Sorting sidebar</li>
<li>Many more</li>
</ul>

Acquaintsoft sidebar generator

Create custom widget configurations for every page/post on your website.

WP Admin Custom Fields vs Acquaintsoft sidebar generator