OpenMx for R
OpenMx is free and open source software for use with R project that allows estimation of a wide variety of advanced multivariate statistical models. OpenMx consists of a library of functions and optimizers that allow you to quickly and flexibly define an SEM model and estimate parameters given observed data.
OpenMx runs on Mac OS X, Windows, and several varieties of Linux. This means the same scripts you write in Windows will run in Mac OS X or Linux.
OpenMx can be used by those who think in terms of path models or by those who prefer to specify models in terms of matrix algebra. OpenMx is extremely powerful, taking full advantage of the R programming environment. This means that complicated models and data sets can be specified and modified using the R language.
Click for the revised Introduction of the Documentation.