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...
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
SoftPerfect Network Scanner - Powerful multipurpose network administration tool for Windows and macOS
Wifi Analyzer - Wifi Analyzer is a handy tool which helps you to select a better channel for your wireless router.