Simile is a system dynamics modeling program, developed at the University of Edinburgh and spun out as a commercial product to the company Simulistics.

Simile provides a visual interface to continuous-systems modelling using system dynamics (stock-and-flow) notation, and also provides sophisticated features for handling disaggregation (e.g. spatial grids, populations of individuals, etc). The graphical system dynamics notation allows the underlying differential equations defining the simulation to be defined in an intuitive graphical way and then solved using inbuilt differential equation solvers. Simile generates C++ code for simulating model behaviour (hence is computationally efficient).

It can be driven by a scripting language, SimileScript, which is a Tcl interpreter with custom commands added.

Simile's spatial modelling facilites make it well suited to modelling ecological systems, but it is also capable of doing the things other system dynamics packages can do.