httpbin(1) - HTTP request and response service
HTTPDump - A simple, beautiful Webhook debugging tool.
Endpoints - View and respond to requests on an HTTP endpoint
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
Beew.io - The simplest way of scheduling HTTP requests.
Rollout - Fix or prevent critical bugs while your app is live.