Siege engines in DF haven’t been updated since the game was 2D, and can only aim in four directions. To make them useful above-ground, this plugin allows you to:
link siege engines to stockpiles
restrict operator skill levels (like workshops)
load any object into a catapult, not just stones
aim at a rectangular area in any direction, and across Z-levels
You can use the new features by selecting a built siege engine and running gui/siege-engine.