GNUPlot

GNUplot es un programa para generar gráficas de funciones y datos. Es compatible con la mayoría de los sistemas operativos mas populares(Windows, Linux, Unix, etc).

Gráfica funciones simples utilizando interfaz web: http://toycompute.net/?page_id=55

Pueden encontrar la documentacion oficial del programa (mucha información) aquí.

Lo básico

Funciones Permitidas

 __________________________________________________________
      Function            Returns
      -----------      ------------------------------------------
      abs(x)            absolute value of x, |x|
      acos(x)           arc-cosine  of x
      asin(x)           arc-sine    of x  
      atan(x)           arc-tangent of x
      cos(x)            cosine      of x,  x is in radians.
      cosh(x)           hyperbolic cosine of x, x is in radians
      erf(x)            error function of x
      exp(x)            exponential function of x, base e
      inverf(x)         inverse error function of x
      invnorm(x)        inverse normal distribution of x
      log(x)            log of x, base e
      log10(x)          log of x, base 10
      norm(x)           normal Gaussian distribution function
      rand(x)           pseudo-random number generator      
      sgn(x)            1 if x > 0, -1 if x < 0, 0 if x=0
      sin(x)            sine      of x, x is in radians
      sinh(x)           hyperbolic sine of x, x is in radians
      sqrt(x)           the square root of x
      tan(x)            tangent of x, x is in radians
      tanh(x)           hyperbolic tangent of x, x is in radians
      ___________________________________________________________
      Bessel, gamma, ibeta, igamma, and lgamma functions are also
      supported.  Many functions can take complex arguments.
      Binary and unary operators are also supported.

Link con más nociones básicas y ejemplos de utilizacion del programa: http://people.duke.edu/~hpgavin/gnuplot.html