Features

A rich graphical user interface lets you quickly tackle one-off problems.
For more elaborate tasks, the intuitive command language makes script writing easy. For example, to graph two data vectors x and y against each other, just type "graph x y".
Automatic script-writing mode will create a script based on your GUI point-and-click actions. Write scripts without typing a single command!
Data manipulation is easy with Extrema's automatic expression evaluation. For instance, if you have 10,000 (x,y) data coordinates stored in vectors x and y, you can instantly compute each of their distances from the origin with "d = sqrt(x^2 + y^2)".
Simple, easy-to-understand programming constructs allow you to write code with little or no programming experience.
The GUI gives you ALL the power of the low-level language, and vice versa.

Contour plots: colour, legend, area/volume tabulations, control over contour label size, colour, separation, etc.
Density plots: derivatives, random point type, box type, colour filled regions, dithering patterns with automatic or user defined patterns, diffusion type, profiles, legend, area/volume tabulations, etc.

Customized 2-D line graphs, scatter plots, horizontal or vertical bar charts, each with a large variety of type styles and fonts of any size and color
Customized or automatic legends
Multiple axes with arbitrary axis positioning
Fill the area between data curves or fill individual histogram bars
Logarithmic axes, to any base, including e
Axis scaling can be automatic or user set (including commensurate axes)
Labels can optionally follow the curves on rescaling a graph
Many plotting symbols, with control over size, colour and angle
Complete control over axis appearance (short/long tic mark length and angle, separation between tic marks and axis labels, axis angle, length and location, axis labels size, colour, font, number of digits, etc.)

Differentiate/Integrate an arbitrary expression
Interpolate 1-D or 2-D data using various methods (linear, Lagrange, weighted splines under tension, Fritsch-Carlson, etc.)
Smooth data using various methods (weighted splines under tension, Savitzky-Golay filters, etc.)
Convolution and deconvolution of data
Integral transforms of arbitrary expressions
Fast Fourier Transforms and Inverse FFT's
Reorganize data (sort, step, roll, wrap, etc.)
Weighted (re-)binning of 1-D or 2-D data into automatic or user defined bins (specified by centres or edges)
Find multiple real roots of an expression
Recursive and non-recursive digital filters
Manual or automatic determination of data extrema using graphics cursor
Fit data with an arbitrary, non-linear, expression involving up to 25 variable parameters
Ellipse fitting
Calculation of parameters for least-squares fit using adjustable parameters
User defined and named variables (scalars, vectors, matrices, strings, arrays of strings)
Full indexing on variables and expressions
Literal vectors may be specified as a list or a range
Boolean operators (<, >, &, etc.)
Array operators (inner/outer product, matrix transpose, etc.)
Over 200 built-in functions including: scalar type (Bessel, Clebsch-Gordan, etc.); array type (sum, product, loop, where, etc.); string type (case, date/time, etc.)
Mathematical/character expressions may appear in any suitable command parameter
Use character variables to substitute for complicated expression substrings

Display the history of variables
Read data from binary or ASCII files by formats or space/tab/comma separated columns
Output data to binary or ASCII files by formats or in columns
Dynamic allocation of arrays
Digitize data from a displayed plot

Scripting capability with up to 20 nesting levels and with parameter passing
Script library of `super' commands
Nested looping, branching and conditional statements in scripts
Display messages, prompt for user input from within a script
Return to interactive mode from within a script, and later resume script execution
Create a script interactively

Comprehensive on-line documentation: instant help for any command, or interactive browsing through help library
Keyword searching
Save/Restore an entire Extrema session, including graphics
Keep a journal file of all command input and message output
Dynamic input line recall buffers allow recall/edit of commands using the arrow keys