Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
BlueCat DDI - Unify your DDI (DNS, DHCP and IPAM) solutions to make DDI data an engine for innovation and growth.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
phpIPAM - phpipam is an open-source web IP address management application (IPAM).
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
ManageEngine OpUtils - ManageEngine OpUtils is an IP address and Switch port management software that includes a comprehensive set of 30+ tools that helps network engineers monitor, diagnose and troubleshoot their IT resources.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.