Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.

The Dude - MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of the countries around the world.

Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use

Pandora FMS - Pandora FMS: Opensource monitoring software

Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.

OpenNMS - Project home page of OpenNMS - a java based network managememnt platform developed under the Open Source model