Any ~Star Wars style~ laser guns where you can see the projectile. (Arrows that arc in their trajectory for example and stick in their targets).
I would love to know how to make a gun that shoots say ...cannon balls.. so you could see their trajectory for example. The current Bows may as well be guns IE the arrows just appear at their targets. It's be great for an old western style game/ninja game etc...as would a visible laser bolt for sci-fi games.
I can't code for the life of me in LUA (yet), but this would be a great start if anyone knows where to find such code if it exists.
Maybe this might be with GameGuruMax?.. fingers crossed.