http://www.mathtrench.com

It provides a broad collection of solved math problems, with complete and detailed solutions. A very complete and diverse array of topics included, such as Algebra, Calculus, Statistics and many more, together with more technical math subjects...

http://www.digitalCalculus.com/demo/curvfit.html

CurvFit is a nonlinear curvefitting program: Lorentz, Sine, Damped Sine, etc. series are available models to match data. A Lorentz series is highly recommended for multiple peaked and/or valleys data. Interpolation & extrapolation options are available...