Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
SonicWall - SonicWall security solutions protects your network, systems, users and data from cyber threats.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
Emsisoft Online Armor Firewall - Emsisoft Online Armor Firewall is a freemium online firewall protection system by the Emsisoft that is based on the own independent protection technology of the Emsisoft.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
TinyWall - Lightweight and non-intrusive firewall
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.