Command Block

The Adventure Mode Control Block (name might not be final ) is a block that will be added in a future update. It is being made with the intent to support Adventure mode and will allow mapmakers to expand the interaction with the player through server commands. The block can run specified server commands when activated by redstone current. Considering its functionality, they will not be able to be crafted and only administrators will be able to place them.

Commands
Note: This is only speculation on what the commands could be, as the block does not exist yet.

/gamemode - Could be useful in adventure maps to allow the player to fly

/tp - Could be used as a game mechanic to get the player around the map, but also to make working teleporters

/give - May not be needed as dispensers work just as well, but dispensers can only hold so many items, and the player has to be in front of it.

Usage
The AMCB (Adventure Mode Control Block) will execute server commands like giving items or experience to a player.

History
On July 27th, 2012, Jeb began tweeting of a new block he had created to start expanding Adventure mode. He began posting pictures, ideas and hints of what the block will be able to do.