Alternative uses of a blockchain-mechanism?
Provably fair games can utilize it. For example, Satoshi dice published the hash of their daily secretkey hash list in the blockchain. In that way, they can prove that they haven't altered they secret key list. Or you could do a simple "guess a number" game that kept an encrypted copy of the result in the blockchain. Later reveal the secret key and 

Essentially any kind of system that relies on the escrow of a small amount of information could use the blockchain for that escrow. You could even use it to as a communication channel if your messages were small enough.