Fping (open source) - fping is a program to send ICMP echo probes to network hosts, similar to ping, but much better performing when pinging multiple hosts.
WinPcap - Industry-standard tool for link-layer network access in Windows.
Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.
Npcap - Npcap is the Nmap Project's packet sniffing library for Windows.
OpenSpeedTest - Broadband Internet Speed Test Unlocked!
Proximac - An open-source command-line program for Mac OS X to make any app work through a proxy server.