WireMock : Free and Open Source tool for building mock APIs. Create stable development environments, isolate yourself from flakey 3rd parties and simulate APIs t...
httpbin.org : A simple HTTP Request & Response Service.
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...
gRPC : gRPC is a modern, open source remote procedure call (RPC) framework that can run anywhere. It enables client and server applications to communicate tr...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Mockoon is the easiest and quickest way to design and run mock APIs. No remote deployment, no account required, free and open-source.