A free cross-platform library of fast C++ routines for the plotting of up to 3-ranged data. It can export to bitmap and vector EPS/SVG files. There are window interfaces (GLUT/FLTK/Qt) and console tools. MathGL can be used from C/Fortran/Python/Octav/Lua
Netkit is a network emulation environment that allows the user to setup complex scenarios on a single PC with little effort and at no cost. In itself, Netkit aims at integrating different other open source products to provide an easy-to-use interface.
...It uses Python programming language for definition of its API. Itegrates visual components for limited post-processing. Provides access to some GUI components for more efficient setup the simulation cases.
EP Simulator is a simulation of a cardiac electrophysiology laboratory, complete with recording equipment, programmable stimulator, and, most importantly, a heart simulator that can be setup to mimic normal cardiac electrophysiology and arrhythmias.