patchbay : patchbay.pub is a free web service you can use to implement things like static site hosting, file sharing, cross-platform notifications, webhooks hand...
mail-tester.com : Free online service that allows you to test your emails for Spam, Malformed Content and Mail Server Configuration problems
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
REDbot : REDbot is lint for HTTP resources; it tests protocol correctness, cacheability, content negotiation and more. REDbot checks HTTP resources to see how ...
Differentiate HTTP headers and content body of two GET URLs.
