[dozzie]

First and foremost: blockchain, in its essence, is a document timestamping service. As such, it allows somebody reading it to tell the order of arrival of stored documents (documents themselves being unmodifiable, as they are usually identified by content in cryptography).

It just happens that ledger is a quite good fit for document timestamping, and account balance can be used as a way to transfer money-like values (note that it's not the only way; cryptographers have a history of developing digital money systems).

About the only thing new about blockchain is that it doesn't need a trusted third party (system with rights and means to modify the data) to timestamp documents to defend against adversarial modifications to the timestamps stream.

Anyway, anything that would use ordering of documents/messages could be built on top of blockchain, but calculating proof-of-work is a very steep price to pay for the defense against some of the participating servers being malicious, given that enterprises happily trust regular databases that don't sign cryptographically anything.