Nanospell is an ad-free CKEditor spell check plug-in that offers free developer licenses for PHP, ASP, ASP.Net, and Java. An online demo with the javascript source code is available.

For context, it's important to note that CKEditor does not feature built-in spellchecking on any browser. By default, CKEditor has to disable the default spellchecking behavior to render its menu system. The spellchecking you see with CKEditor by default is sent to a commercial server for processing, and comes with PPC ads.
The affordability and security of the data within a spellchecker plugin is especially crucial for businesses and individuals prioritizing confidential information protection. Spellcheck plugins for CKEditor/FCKEditor have traditionally sent data off-site to Google or other service providers, but the SpellCheck plugin from NanoSpell is quite different. This plugin conducts all spellchecking on your server, surpassing your firewall. This aspect proves particularly useful for enterprises with secure intranet, extranet, or admin areas on their site.
NanoSpell's spell-checking technology is nearly platform independent. It can easily install on Linux, UNIX, Windows, 'OS X', and BSD operating systems. What's more, it supports a variety of web servers, including Apache, TomCat, NginX, Microsoft Windows IIS, and IBM WebSphere. Back-end languages it supports include PHP, ASP (Active Server Pages VBScript), ASP.Net (C#, VB.Net and more), and Java.
Overall, CKEditor SpellCheck from NanoSpell provides an easy-to-use, secure, and cost-effective solution for CKEditor User's spellchecking needs.
Version 1.1.141211:
Newley released independant spellcheck plugin for CKeditor.
Download the plugin and free international dictionaries from http://ckeditor-spellcheck.nanospell.com