Waircut - Free network audit app
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Ekahau HeatMapper - The Free Wi-Fi Coverage Mapping Site Survey Tool
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
iBwave Wi-Fi - iBwave Wi-Fi software suite brings smart networking solutions to enterprise, education, hospitality, transportation, retail, office, healthcare, public venues, and residential wireless networks.
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use