Even during a model run, ExtendSim parameters and model logic can be changed "on the fly" rather than having to wait until the simulation ends. This means you can get fully involved with an ExtendSim model, even play with it, and leave no alternative unexplored. ExtendSim's point and click interactivity translates into faster answers and winning solutions.

You can create, reuse, even distribute ExtendSim blocks – the components that comprise a model. Group existing blocks to save them as one hierarchical block. Or develop custom blocks with unique behaviors, icons, and dialogs. Store your new block in an ExtendSim library for reuse in other models or for distribution to others. Block reusability increases productivity, improves consistency of design, and avoids having to reinvent the wheel each time you build a new model.

Because of its powerful constructs and unlimited hierarchical structure, ExtendSim is the simulation tool of choice for producing complex, accurate enterprise-wide models, while remaining practical enough to build small to mid scale models. Plus, ExtendSim gives you the option to add more flexibility in the form of third party modules and companion products. With ExtendSim, you always have full capability to model any size project.

Block icons convey the structure and behavior of the model at a glance. In ExtendSim, both the flow of items and the flow of values are graphically represented. This unique mapping of visual meanings into their equivalent icons promotes quick understanding of a model to anyone viewing it.

ExtendSim has an integrated relational database and supports COM/ActiveX and ODBC. Dynamically link data to an ExtendSim database, embed an Excel spreadsheet in a model, control an external application, or have the other application control ExtendSim. These technologies have been implemented as modeling components so that communication within ExtendSim and between applications are drag-and-drop operations, with no programming necessary.

ExtendSim block components are developed using its compiled language and integrated development environment. They are Open Source to allow modification and enhancement. You can alter existing blocks and develop new proprietary components for distribution to internal or external customers. Linking to code and routines written in external languages is also supported. ExtendSim's open source architecture gives you the freedom to model anything.

ExtendSim is so flexible it has become the simulation engine used by most OEM developers and the learning tool used by most educators. This expands ExtendSim’s reach around the globe. That’s why you will find ExtendSim in so many applications, products, and textbooks.

ExtendSim was the first simulation program to successfully bring simulation to the desktop. Originally released as Extend in 1988, ExtendSim brought capabilities to analysts that were previously available only to mainframe computers. 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.

	1988	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
	1992	First hierarchical modeling capability for nested submodels First message-based discrete event architecture
	1995	First Windows/Macintosh simulation system
	1998	First scripting capability so graphical models could also be created, populated, and run programmatically
	2001	First open source Optimizer First drag and drop ActiveX/COM support
	2002	First integrated FTP support for internet data exchange
	2007	First use of LP technology to provide global oversight for calculations in mixed discrete event/discrete rate models