Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
cPanel - With its first-class support and rich feature set, cPanel & WHM has been the web hosting industry's most reliable, intuitive control panel since 1997.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
Webmin - Webmin is a web-based interface for system administration for Unix.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
Vesta Control Panel - – What I love about Vesta is that it's fast and easy to use
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.