Dropper

The dropper is a block that drops an item from its inventory as an entity (as if it were dropped by the player) each time it is powered. If there is a chest immediately in front of the dropper when it is powered, it will instead store the item within. A dropper can drop items through a glass block in front of it.

This is in contrast to a dispenser, which behaves differently with certain items, such as firing projectiles, placing liquids from buckets, and spawning mobs from spawn eggs. Dispensers also do not store items in chests.

Trivia

 * By placing droppers so that they feed into each other, similar to a hopper pipe, and powering each of them and updating them with a 1 tick clock, Minecraft's fastest item transport system can be produced, with the advantage of going all 6 directions, at a speed of 10 blocks per second. This means that if you have a 100 block long dropper pipe, items going in on one end will pop out the other end in only 10 seconds.
 * This is twice as fast as a hopper pipe, however, two hopper pipes side by side take up less space, and make no sound.
 * Dropping a block directly into a cobweb placed in front of it will mean that the time for the block to pass through the cobweb will be approximately half of the delay for dropping the block on top of the cobweb. This is useful for a 10-12 second delay redstone trigger.