It is inspired by Sjoerd Visscher's XML-RPC Client for David Adams' XML-RPC Speller service, however it is different in that it does not involve an active middleman1.
The backend XML-RPC service is written in PHP and uses Useful Inc's XML-RPC to wrap pspell (which is link against PHP 4.0.62).
1 - Sjoerd Visscher's implementation appears to make requests through his web server and return the results as Javascript arrays. Since his web server is doing work on the XML to transform it into a JS I call it a middleman. XSpell passes the XML back to the web browser directly and the JS must parse it - hence no middleman.
2 - with pspell and aspell compiled, installed and working... pspell can be linked against your PHP by compiling with the .configure --with-pspell=/usr/local/lib switch.