httpbin.org : A simple HTTP Request & Response Service.
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
mountebank : mountebank is the first open source tool to provide cross-platform, multi-protocol test doubles over the wire. Simply point your application under tes...
Webhook Tester : Webhook Tester allows you to easily test webhooks and other types of HTTP requests.
Postal : Postal is a complete and fully featured mail server for use by websites & web servers. Think Sendgrid, Mailgun or Postmark but open source and ready f...
MailHog is an email testing tool for developers:
Configure your application to use MailHog for SMTP delivery
View messages in the web UI, or retrieve them with the JSON API
Optionally release messages to real SMTP servers for delivery