Unleash - Open source Feature toggle/flag service. Helps developers decrease their time-to-market and to increase learning through experimentation.
httpbin(1) - HTTP request and response service
LaunchDarkly - LaunchDarkly is a powerful development tool which allows software developers to roll out updates and new features.
HTTPDump - A simple, beautiful Webhook debugging tool.
ConfigCat - ConfigCat is a developer-centric feature flag service with unlimited team size, awesome support, and a reasonable price tag.
HTTP Prompt - An interactive command-line HTTP client