Music Block

Music Block is a block-type that was planned for the Beta release, but is not yet available in the current build.

Quoted by Notch in a Jan. 6 blog post, "Oh, and I’ve finally committed the Music Blocks to the repository. (Oh, wait, no, I didn’t.. Doing so broke git, so we’re changing to svn because git is horrible and evil)"

It appears that Music Blocks will be a new type of block, and will allow users to create musical notes within the game.

In response to a question about how they work, Notch said: "right click to tune (2 octaves). Left click or redstone trigger to play. The material under the block sets the instrument" Notch recently stated that: "Woops, note blocks don't play in multiplayer.. *fixificates*"

which would seem to indicate that music block (or note blocks) are either complete, or nearly complete, and will likely be included in the promised Jan 13 update.

It is unknown where Music Blocks will be found, or how they'll be crafted.