Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
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
Yellow Lab Tools : Online test to help speeding up heavy web pages
MindMeister : MindMeister is an online mind mapping tool that lets you capture, develop and share ideas visually.
Differentiate HTTP headers and content body of two GET URLs.
