Implement the game of life in 3D
Mathematica - 120 bytes

g=CellularAutomaton[{(l=Flatten@#;c=l[[14]];n=Total@Drop[l,{14}];Which[n&lt;2||n&gt;7,0,n==5||c==1,1,0&lt;1,0])&amp;,{},{1,1,1}},##]&amp;


Certainly not a contender for the win, but that was not my intention. Also, this could probably be golfed down significantly by just figuring out the rule number. I just really wanted to write a visualisation (although I'm actually sure there are already tons out there). So here we go):

animateGol3d[size_, i_, n_] := 
  ListAnimate[
    Graphics3D[
      Cuboid /@ Position[#, 1], 
      PlotRange -&gt; {{0, size}, {0, size}, {0, size}} + 1
    ] &amp; /@ g[i, n]
  ];


And after experimenting with a bunch of initial conditions, I got things like the following:



And here is one with a grid size of 20x20x20. This took a few seconds to simulate and render:



By the way, this assumes periodic boundary conditions.