NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
JPerf - This project gives a better UI and new functionalities to the initial JPerf 1.
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.
NetStress - NetStress is a user-friendly benchmarking tool that is mostly used by networking professionals to measure the network performance of both wired and wireless connections.