Greg - SiteOrigin

I built this plugin to help ease the transition during a DNS changeover, but you can use it any way you please. It turns your WordPress installation into a very simple proxy server. It fetches content from another URL, caches it and displays it. Requests are cached for 24 hours.
Install the plugin, then head over to Settings > Simple Proxy in your WordPress admin. Enter the URL you want to proxy to and when you’re ready to go, also check the enabled checkbox.
You need to have <a href="https://codex.wordpress.org/Using_Permalinks#Choosing_your_permalink_structure" rel="nofollow ugc">pretty permalinks</a> enabled.
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Simple Proxy

Turns your WordPress installation into a simple caching proxy.

TinyMCE SpellChecker API – this plugin provides action/filter hooks to allow easy customisation of the TinyMCE SpellChecker.
This plugin was created to solve the problem of not being able to use GoogleSpell behind a firewall. For background information on the issue read the discussions on <a href="https://core.trac.wordpress.org/ticket/9798" rel="nofollow ugc">trac ticket #9798</a>. The ultimate goal of this plugin is to be merged into WordPress Core.
You need this plugin if…
<ul>
<li>You want to write a plugin for the TinyMCE SpellChecker. This plugin will provide you with respective hooks that allow to control which SpellChecker Engine is used, adjust the configuration used for initialisation of the engine and manipulate spellchecking results (independent of engine).</li>
<li>You are behind a firewall and you’d like to use the Google Spellchecker. This plugin contains a customised version of GoogleSpell that uses the new Http Transportation methods added in WordPress 2.8 which include Proxy Support for all external requests.</li>
</ul>
This plugin also contains a simple sub-plugin called “WP-SpellCheck Exceptions” which allows you to add custom words to the spellchecking dictionary. Note that this plugin is more a proof of concept than a complete/full-fleged solution. (It does not have any kind of visual administration; it only adds “WordPress” as an exception at the moment).

WP-Spellcheck

TinyMCE SpellChecker API - this plugin provides action/filter hooks to allow easy customisation of the TinyMCE SpellChecker.

Simple Proxy vs WP-Spellcheck