Good News (November 2003): Brown University has changed the licence on fnord to GPL so it is finally truly open source. Thanks!

• manual
• FAQ from Brown
• source code
• sparc binary
• SGI irix 5.3 binary (needs the source)
• linux elf binary (needs the source and the motif shared lib if you don't already have motif)

Thomas Banchoff (who advised its creation) uses fnord to teach calculus, geometry, and topology (see his projects list)

circle := R -> (R, R)
       :  t -> (cos t, sin t) / sqrt(2);

I := Interval(-pi, pi, 31);
J := Dashes(-pi, pi, 31);

flatTorus := [ circle(I) >< circle(J) ];

project := R^4 -> R^3
        :  [x, y, z, w] -> [x, y, z] / (w - 1)
        ;

A := [[cos a, 0, 0, -sin a],
      [    0, 1, 0,      0],
      [    0, 0, 1,      0],
      [sin a, 0, 0,  cos a]]
  ;

rotate := R^4 -> R^4
       :  x   -> A x
       ;

a := widget Slider(0, pi/2), name<-"rotation around XW plane";

widget Show(project(rotate(flatTorus)));

SecondFundamentalForm
   := Surfaces -> (R^2 -> R^2^2)
   :  X        -> (u   -> let n be SurfaceNormal(X)(u) in
		   [[X''(u)^1^1 . n, X''(u)^2^1 . n],
		    [X''(u)^1^2 . n, X''(u)^2^2 . n]])
   ;