Are there any non-monetary uses for the blockchain, or the Bitcoin protocol generally?

Question

After reading "Have there been attempts at a Bitcoin-powered general purpose database?", I'm wondering if any other uses have been made (or proposed) of the blockchain and Bitcoin protocol that aren't solely about financial transactions (and directly related activities like mining)?

(Perhaps something similar to Bitmessage, but using Bitcoin itself rather than simply taking inspiration from it.)

Answer 1

• The blockchain basically implement a time-stamp infrastructure. Here are some examples: search for "Satoshi Proof Android" and "BTProof"
• SPAM mitigation: "BitcoinPayment is a MediaWiki extension to limit spam, by requiring a small one-time bitcoin payment before a user is allowed to edit or create pages. While the payment is deliberately trivially small for a normal user, it presents a barrier to a mass-spammer."
• Online identity/reputation management: search for "Keyhotee"
• Voting mechanism

Those are only a few I can think about right now.

Answer 2

Proof of Existence is a good example of innovative use of Bitcoin network. The idea is as follows:

use our service to anonymously and securely store an online distributed proof of existence for any document. Your documents are NOT stored in our database or in the Bitcoin blockchain, so you don't have to worry about your data being accessed by others.

More details: http://www.proofofexistence.com/about

Answer 3

Since the blockchain is a publically verifiable ordered list of transactions, many (but not all) registries, for which we currently trust a central organisation, and pay fees, could be replaced by a bitcoin-like blockchain. A typical example, for names, is Namecoin.

I said "many", not all, because registries can also ensure other services, besides "pure" registration.