TrafficMonitor - TrafficMonitor is a network monitoring suspension window software in Windows.
Speedtest by Ookla - Measure your ISP's performance in a click
NetSpeedMonitor - NetSpeedMonitor is a lightweight Network Monitoring Toolbar for your Windows Taskbar
TripMode - Manage your Mac's broadband usage while on a hotspot
FreeMeter - Monitor network bandwidth (C#.NET 2k/XP+). Desktop and Systray graph.
Slowy app - Simulate custom Internet connection speeds for testing