ExtendSim has been an innovator and leader in the simulation field for over 25 years

ExtendSim was the first simulation program to successfully bring graphical simulation to the desktop. Originally released as Extend in 1988, ExtendSim brought capabilities to analysts that were previously available only to mainframe computer programmers. The vision which led to the first graphical simulation environment continues today. In the process of developing and enhancing ExtendSim, Imagine That! has scored a number of 'firsts' in the simulation industry.


First application designed as an integrated simulation environment (graphical user interface for model building integrated with a simulation programming language)

First template-based (library) simulation system

First open source modeling components


First hierarchical modeling capability for nested submodels

First message-based discrete event architecture that is the blueprint for modern simulation software. The technology pioneered in ExtendSim is used now being used by Simul8, AnyLogic, Simio, FlexSim, Simulation Studio, and more. Products that were developed before ExtendSim or at the same time as ExtendSim (Promodel, Arena) do not have this.


First Windows/Macintosh simulation system


First scripting capability so graphical models could also be created, populated, and run programmatically.


First open source Optimizer

First drag and drop ActiveX/COM support


First integrated FTP support for internet data exchange


Integrated internal relational database introduced

Invented discrete rate technology

First use of LP technology to provide global oversight for calculations in mixed discrete event/discrete rate models


First integrated Advanced Resource Management (ARM) system

First implementation of database variables for scenario management - sets of data, rather than just single variables, can be used as factors and responses.


First use of attributes to track properties of continuous flow in a discrete event environment.

As you can now see, ExtendSim developers are constantly coming up with amazing new features to keep ExtendSim at the top of the simulation heap.