That's it, a couple of searches via Google, and nothing as expected ... but hey, wait a minute: what's about FireFox spell checker plug in and Open Office project? Here we are, Hunspell is the answer!
In a full day of self brain storming, history background cases study, and code, plus debug and tests, I created BJSpell, a basic, fast, cross browser, and runtime implementation capable to underline bad words using a pre compiled Hunspell compatible dictionary (one or more).
The reason I avoided the usage of the classic "click here for the spell checker" is server stress, since the idea was to bring the spell check inside text-areas without polling with short of big texts the server and every N seconds or, the worst case scenario, on every "onkeyup" textarea event!
A real world example page
I created a folder in my website with a BJSpell demonstration page ... wait for the cursor in the right area and try, for example, to write something like "... let's try some weirf word ..."
If you have FireFox spell check plugin with english dictionary, you will difficulty spot the difference between the left textarea and the produced output in the right div ... but what the plug-in does not do, is to show you a couple of alternatives, or close words, instead of the wrong one
The project is in beta status, so I need your help to debug it and to understand if it has been worthy and if it is truly a good compromise between performances and result. The suggestion is not perfect, truly quick and dirty, just a basic and incomplete implementation, so we will see how and if the project will go on ;-)