spell checker

I'm not sure what the point would be, most browsers include one now.

Firefox and konqueror do it without you doing anything. I'm not sure
about IE and safari.

Google showed me these for ruby, although I haven't used them:

http://deezsombor.blogspot.com/2005/08/how-to-build-ajax-ed-spellchecker-with.html
http://www.maxkiesler.com/index.php/comments/ajax_and_ruby_on_rails_based_spellchecker_demo/