ExtendSim is a workbench style simulation tool that supports the development of discrete event, continuous, discrete rate and agent based models. The image below shows a simple discrete event model from the extensive library of example models provided. To the right is the Item library which is used to build discrete event models.


ExtendSim is NetMod’s chosen simulation tool for a large number of reasons and we believe it has the many benefits that we list below. Nevertheless there are many other good tools out here that are supported by highly professional specialists and consultants. Some of these will have features very well suited to particular applications.

Why we like ExtendSim:

  1. Natural modelling paradigm that makes it easy to learn. Engineers love it!
  2. Very mature block libraries with rich functionality.
  3. Most productive environment for modelling that we have seen. Amazing what you can model in a short period of time.
  4. Excellent documentation with comprehensive supporting material including example models.
  5. All library blocks can be examined at the code level and can be modified to create new blocks that change or add functionality.
  6. Fully featured programming language (ModL) which  can be used as in 4 but also in special blocks that allow code snippets.
  7. Good run-time performance and scales well to models with large numbers of blocks (thousands!).
  8. Excellent connectivity. Supports COM, DDE, FTP, ODBC, ADO and allows external DLLs to be called. Data can be imported/exported to Excel or flat files.
  9. Highly efficient internal database  capability that is almost indispensable for large models.
  10. Ability to build your own block libraries allows the development of custom modelling tools that may look quite different to the standard libraries.
  11. Cost for a fully featured package is very low and run-time licenses are either free or nearly so. 

Of course no tool is a perfect fit for everyone so we will list a few ‘niggles’ although Imagine That have some exciting plans for version 10 that should consign most of these to history.


  1. The interface is a little dated and standard animation although very useful is not very smooth.
  2. Certain extremely large models can run slower than expected although we have coded some custom blocks that fix this.
  3. The ModL language is relatively low level (similar to plain C) although it does have a vast set of ExtendSim functions.

Users often invest a lot of time learning the way their tool works and developing models and reusable components. This makes it very important to select the most suitable tool at the outset. We believe that ExtendSim is the best general purpose simulation modelling tool out there and are happy to help any organisation with an evaluation free of charge – we will ask you to buy any licenses through us but you do not have to do this.

Help with ExtendSim Evaluation:

  1. Half day on site introduction to ExtendSim.
  2. Example model development.
  3. Tell us what you want to do and we can show you how to do it in ExtendSim.
  4. If external connectivity is important we can offer a lot of experience.