Musicblock
Musicblocks have been described by Tiny Speck as "collectible game items" [1]. They play a short sound track each time you play one.
You cannot make them or buy them from vendors. They are sometimes rewarded with certain actions such as donating to Shrines, squeezing chickens, petting trees and spinning a spinning wheel/gameshow ticket. Many players sell them on the auctions.
If you play them, you may gain XP and mood rewards. You can also play them for other players if they are close by.
If you collect all the Musicblocks of a certain, you will get a the musicblocktrophy trophy plus rewards.
Musicblocks are popular items for donating to Shrines because they give good favour rewards.
Trivia
Play a single Musicblock too much and it gets 'stale' - each time you play that block from then, you lose a little energy/mood.
The SB-1 Musicblock is the rarest Musicblock, given only by devs to favourited players.