Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
Chocolatey - The sane way to manage software on Windows.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
WAPT Community - Deploy your software and configurations, perform an inventory of your machines in real time, control Windows Updates and benefit from customized reporting of your IT assets
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Just Install - just-install - The stupid package installer for Windows.