Yellow Lab Tools : Online test to help speeding up heavy web pages
HTTP Security Report : Get an instant report of how your website measures up to the best practices.
Check connection encryption, content security, information disclosure and...
Bloody Vikings! : Firefox addon to simplify the use of temporary e-mail addresses in order to protect your real address from spam.
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Requestdiff : Differentiate HTTP headers and content body of two GET URLs.
Free online service that allows you to test your emails for Spam, Malformed Content and Mail Server Configuration problems