WireMock : Free and Open Source tool for building mock APIs. Create stable development environments, isolate yourself from flakey 3rd parties and simulate APIs t...
Matrix : Matrix is an open standard for decentralised communication, providing simple HTTP APIs and open source reference implementations for securely distribu...
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...
httpbin.org : A simple HTTP Request & Response Service.
Grafana k6 : Grafana k6 is an open-source, developer-friendly, and extensible load testing tool. k6 allows you to prevent performance issues and proactively improv...
Mockoon is the easiest and quickest way to design and run mock APIs. No remote deployment, no account required, free and open-source.