PacketFence - PacketFence is a Free and Open Source network access control (NAC) system.
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.
Okta - Enterprise-grade identity management for all your apps, users & devices
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.