Also included is an array of goodness-of-fit measures taken from various sources (Coefficient of Determination, r-squared, Model Selection Criterion), as well as code for calculating the error surface Hessian, and from the Hessian, parameter covariance and correlation matrices. The covariance matrix allows a less rigorous but often more useful method for calculating confidence intervals, as well as means by which to analyze the utility of the parameters in capturing the data fit by the model. This is achieved through use of actual Numerical Recipes in C functions, so you need to acquire a copy of NRC to employ them.
You should be able to compile and use GML with other compilers than the one from Metrowerks. More importantly, this software should run on any architecture, including Mac, PC/Intel or your favourite Unix box. You just need to get the NRC routines onto the platform. I know so because the code has been developed over time on both PC and Mac. :-)
General Overview
Useful Definitions
Detailed Documentation