Fiddler - Fiddler is a debugging program for websites.
NetSpeedMonitor - NetSpeedMonitor is a lightweight Network Monitoring Toolbar for your Windows Taskbar
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
NetTraffic - Essential network bandwidth monitor.
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.
FreeMeter - Monitor network bandwidth (C#.NET 2k/XP+). Desktop and Systray graph.