inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
NetStumbler - Official source of information about Netstumbler.
SoftPerfect Network Scanner - Powerful multipurpose network administration tool for Windows and macOS