GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.

Notepad++ - A free source code editor which supports several programming languages running under the MS Windows environment.

ns-3 - a discrete-event network simulator for internet systems

Sublime Text - Sublime Text is a sophisticated text editor for code, html and prose - any kind of text file. You'll love the slick user interface and extraordinary features. Fully customizable with macros, and syntax highlighting for most major languages.

NetSim - NetSim software was created to simulate various Cisco systems. Cisco software is known around the world as being one of the best network, routing and switch systems for businesses and private use. Read more about NetSim.

Notepadqq - Notepadqq is a linux clone (identical application) of Notepad++