Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
ConfigCat - ConfigCat is a developer-centric feature flag service with unlimited team size, awesome support, and a reasonable price tag.
Endpoints - View and respond to requests on an HTTP endpoint
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
Prefab.Cloud - Change Log Levels without restarting. Feature Flags. Dynamic Configuration. Focus on reliability and powerful features, but radically cheaper than alternatives.