httpbin(1) - HTTP request and response service
Bashupload - Upload files from command line to share between servers
HTTPDump - A simple, beautiful Webhook debugging tool.
FilePizza - Open source application used to transfer file via WebRTC and WebTorrent.
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
BlackHole File Transfer - Blockchain-based file transfer. Designed for everyday use.