NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.
Prometheus - An open-source systems monitoring and alerting toolkit.