Checks the syntax of all changed ruby files is valid before allowing a commit
Validate VAT number via a simple REST API. Returns JSON true/false or JSONP. Uses Google App Engine - by Aral Balkan
Standards compliant HTML cleaner in PHP
Check your HTML email campaign in multiple email clients
Cal Henderson provides an RFC822 complient email validation function for PHP. Also included are links to Ruby and Python versions of the same.
Simple form validation using Ajax