Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Instabug - The top apps in the world rely on Instabug for beta testing, user engagement and crash reporting.
HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
Sonar by Facebook - Extensible mobile app debugging for iOS and Android
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface
Buglife - Seriously awesome bug reporting for iOS apps