A knife has half the durability of a sword and does less damage. It has a small knockback and can be crafted without a workbench.
By right clicking, you can toss the knife like a throwing knife, causing damage to any entity you might hit, the knife can be picked up similarly to an arrow that hit a block.
The knife can be crafted from any of the vanilla weapon materials, i.e. wood, stone, iron, gold and diamonds.
Wood: 3 Damage (1 1/2 Hearts)
Stone: 5 Damage (2 1/2 Hearts)
Iron: 7 Damage (3 1/2 Hearts)
Diamond: 9 Damage (4 1/2 Hearts)
Gold: 3 Damage (1 1/2 Hearts) Has bigger knockback.