k0tik

The usual Text widget allows you to insert arbitrary Text and/or HTML code. This allows that too, but also parses any PHP or JavaScript code in the text widget and executes it.
This plugin is based on “PHP Code Widget”, but now available for use by site administrators ONLY, which makes it more secure.
All PHP code must be enclosed in the standard php opening and closing tags ( <code><?php</code> and <code>?></code> ) for it to be recognized and executed. Also JavaScript code must be enclosed in the <code><script></code> and <code></script></code> tags, as usual.

Safe PHP Code Widget

Adds a secure and simple widget in which you can use PHP and JavaScript code. Also you can use unfiltered HTML or just Text. Admin Use Only.

Justin Tadlock

Hybrid Hook is a plugin that allows end users the ability to tap into the <a href="https://wordpress.org/extend/themes/hybrid" title="Hybrid WordPress theme framework" rel="ugc">Hybrid theme’s</a> extensive hook selection by providing a user interface in the WordPress admin for adding custom content.
You must be using at least version 0.9 of the <a href="https://wordpress.org/extend/themes/hybrid" title="Hybrid theme" rel="ugc">Hybrid theme</a> for this plugin to work. It will also not work with any other themes.
Features:
<ul>
<li>Ability to add custom HTML nearly anywhere on your site.</li>
<li>Use shortcodes to quickly add content.</li>
<li>Allows the input of JavaScript.</li>
<li>User can select the priority the code will run.</li>
<li>Can execute PHP code if the option is selected.</li>
</ul>

Hybrid Hook

Allows the addition of HTML, shortcodes, PHP, and/or JavaScript to the Hybrid theme's hooks from the WordPress admin.

Safe PHP Code Widget vs Hybrid Hook