RF21 is a Mathematics Software that lets you create your own libraries! Since there is always something missing one would like to see, adding user defined functions is supported. So you can create and permanently install all kinds of functions: single- or multivalued, composed of one or several formulae, computed by simple evaluation, by recursion or by numeric integration, or by the Runge-Kutta method. Add comments and save your functions to libraries! Then use them as building blocks for more advanced functions. The program will find, load and reassemble each user function (including user defined components) whenever a call to that function is issued. All you have to do is remember the function name.

RF21 Features
Advanced predefined functions
User defined functions and libraries
Multivalue functions supported at syntax level
Fast execution
Integrated user function database
Simple and parametric plots
Prints plots or exports them to -.GIF files
Numeric differentiation / integration
Finds zeroes, poles, extremal points etc.
Matrix inversion and linear equations at syntax level
Nonlinear function minimizer (Dennis & Schnabel method)
Nonlinear equation system solver
Monte Carlo simulations
Fraction recognizer
Accelerated infinite summation
Runge-Kutta numerics for differential equations