So am I the only one who, reading about minecarts having parabolic arcs and crashing into the ground started wondering how hard it would be to set one up on rails on a looooooonnnnngggg incline to nothing and hit goblins with it? In an aiming sense, of course.
This is the Bay12 forums, is it not? I'm already thinking of setting up minecart launchers in a cliff face, to deal with sieges. Dwarves hop in the minecarts, they then go down a path to get some speed, before shooting out the hole in the cliff face and hopefully crashing down into the invaders, and then the Dwarves themselves get out and do their thing.
Basically, horizontally-launching Dwarven drop pods.
Although, depending on whether or not there's fall damage while in minecarts, you could possibly have them drop down from the sky proper, by setting up what is essentially an Orbital Magma Platform, exept replace the magma with minecarts.
And hey, if that fails, why not load the carts up with some ignited coal, send them on their way and have them fly off and spill their contents all over some grass, to burn the invaders with HOT DWARVEN RETRIBUTION. Bonus points if you instead use ignited corpses of previous invaders of the same race (meaning, Goblin corpses for Goblins attacking you, Elves for Elf attacks, and so on).
Look at that, coming up with ideas for something that's not even fully in just yet.