Weaponry (mod-appropriate)

- Trebuchet
-- range dependant on size (60 blocks for a 9m tall unit)
-- excavates large amounts of material on impact (explosion-resistance-based)
-- no-deletion explosion on impact when non-explosive projectile is used (all blocks drop)
-- LOTS of material to build. would require construction in modules (such as side-frames, arm, sling, weight)
-- either immobile, or buildable on top of minecart(s)

- Ballista (or Arbalest)
(Ballista is a torque-bow, with twisted ropes, Arbalest is a springbow, like a giant crossbow)
-- one-shot any mob, more-aimable than ballista, either immobile or minecart-mounted
-- arbalest requires spring-steel, ballista would require more wood (for the torque frame)
-- explosive darts?

/ - stick , S - string , L - leather , P - planks , I - Iron , G - sling
Component recipes:
Sides:
O / O
/ / /
P P P

Sling:
O O S
O S L
S O O

Swingarm:
O / P
/ P G
P / O

final Recipe: (S - Sides , A - Arm , = - wood halfblock
O A O
S O S
= = =

Triggering would be with a redstone or similar pulse, such as a pressure plate or button.
(would have edited orig post but had idea before I reg'd)