Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
SolarWinds Network Configuration Manager - SolarWinds is a leading provider of powerful and affordable IT infrastructure management software. Make IT look easy.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
Cisco Network Assistant - Cisco Network Assistant simplifies wired and wireless network management, and provides critical product information using Cisco Active Advisor.
Ubiquiti Network Management System - Ubiquiti Network Management System manages all the EdgeMAX, EdgeSwitch, airMAX and UFiber devices.