GNS3 - Cisco Graphical Network Simulator

Introduction
Another great product from open source community. If you have read Dynagen and Dynamips then this will enhance your experience in cisco simulation. GNS3 offers complex graphical network simulator and launch simulation on them.
Features currently supported by GNS 3 are:

Designing high quality complex network topologies.
Emulating Cisco routers and PIX firewalls.
Simulating simple Ethernet, ATM and Frame [...]

LAMP Resources for Network Administrator

Introduction
If you read all the article i submit here regarding the software for network management and monitoring, you will notice that most of them will:

Use Linux/Unix as the Operating System
They need Web Server
They need programming language
And they need database

Someone(s) make a good concept about four things above. They call it LAMP. Linux, Apache, MySQL, Perl/PHP/Python. [...]

ZenOSS - Network Monitoring System

With the vision to deliver open source application for network monitoring system with the enterprise grade, ZenOSS will make you happy. This network monitoring system is suited for fault management, performance management and configuration management. ZenOSS not only support FCAPS term for NMS but also the new generation of ITIL.
There are many kinds of ZenOSS [...]