Meet the Judicator.

This particular model (a tri-barreled gun that fires four TNT projectiles) was inspired by tekkit, because a friend of mine needed a way to launch nukes an effective distance. While that didn't quite work out, this was born. The general design went through about four versions, beginning with a crude (but much smaller) version that had the major disadvantage of completely exposed wiring. Also, you had to remove blocks in order to reload because said friend didn't suggest the door mechanic until version two.

In general, I started work on each new model after the previous one exploded...

The fourth TNT projectile was not added until the final version, by which point I had figured out most of the wiring and added doors for easy loading. It works pretty well. You're not going to get amazing distance with this gun, but it gives pretty concentrated fire and looks cool.

Ideally crewed by 4 men, (two side loaders, one top loader, and one front loader/person to push the button), it can be used by one person. It takes about a minute to load and fire that way though...

Also, if anyone can guess what the namesake of this cannon is, they get 10 points. 10 WHOLE POINTS!

Additional Notes

Although the whole schematic looks nice and polished, this thing actually took quite a bit of work. It took 2-3 fully constructed versions to get it to the point that it didn't blow itself up, and from there had to go through 2-3 more revisions to optimize the redstone circuits. All in all quite a few hours of work for a small Minecraft project, so if you don't mind diamonding, etc, it'd mean a lot!