Yellow Lab Tools : Online test to help speeding up heavy web pages
Litmus : Test and track your emails. Email previews, analytics and spam filter testing.
webhint : webhint is a linting tool that will help you with your site's accessibility, speed, security and more, by checking your code for best practices and co...
Mink : Mink is an open source acceptance test framework for web applications, written in PHP 5.3.
WebScarab : WebScarab is a framework for analysing applications that communicate using the HTTP and HTTPS protocols.
Catches mail and serves it through a dream.
MailCatcher runs a super simple SMTP server which catches any message sent to it to display in a web interface.