Minecraft wiki entry for Development_versions, associated text: Crafted from strings, iron ingots, sticks, and tripwire hooks.
Can be used as a weapon similar to bows.
More damage, more range, takes longer to charge.
Hold to charge, click to release.
Charge is saved in inventory, can be used later.
Can shoot firework rockets holding the crossbow in one hand and the fireworks in the other.
Can be enchanted with new enchantments:
Multishot: Fires three arrows at once in different directions; not compatible with Piercing.
Quick Charge: Increases the reload speed. 3 levels; 0.25 seconds faster each level.
Piercing: Projectiles pierce through mobs. 4 levels; not compatible with Multishot.