EasyEDA - EasyEDA - Web-based EDA suite; runs in browser.
FlexSim - Simulation software to model, simulate, predict, and visualize systems in manufacturing, material handling, healthcare, warehousing, mining, etc.
LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
ns-3 - a discrete-event network simulator for internet systems
TINACloud - Create Simulate and Design Circuits and their PCB layout with TINACloud
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.