Simfit is a free Open Source Windows package for simulation, curve fitting, statistics, and plotting, using a library of models or user-defined equations. Simfit has been in continuous development for many years by Bill Bardsley of the University of Manchester. Although it is written for Windows, it can easily be installed and used on Linux machines via WINE.

Simfit is developed using FTN95 Fortran Compiler and is currently featured on their website as a . The graphical functionality in Simfit has been released as a Fortran library called which allows the programmer to produce charts and graphs with just a few lines of Fortran. A version of Simdem is shipped with the Windows version of the NAG Fortran Builder.[2]

A Spanish-language version of Simfit is maintained by a team in Salamanca.