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.
Wifi Analyzer - Wifi Analyzer is a handy tool which helps you to select a better channel for your wireless router.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services