A must read.
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And it opens up a whole range of possibilities:
Decentralized voting (e.g. Agora), where voters pay using a crypto-currency into an account representing their choice, with the winning candidate being one with highest balance.
Decentralized Domain Name Registration (DNS) (e.g. Namecoin) would be based on a crypto-currency model, and operate independently of ICANN (so technically immune from Internet censorship). Namecoin uses the .bit top-level domain.
Decentralized storage (e.g. Maidsafe and Storj), where trustless nodes would work together (using crypto-currencies as means of payment) to exchange storage space and bandwidth.
Smart self-validating contracts for real-time revenue sharing (e.g. Secure Asset Exchange); helping artists secure and verify their digital artwork by logging it in the block chain (e.g. Monegraph); and even decentralized Twitter-like P2P asynchronous messaging platforms (e.g. BitMessage and Twister).
Document certification (e.g. Proof of Existence) is a clever use of the block chain as a publicly visible and authenticated timestamp.
In fact, asset registries/keys that could theoretically be implemented in a block chain model are endless — land titles, private equities, mortgages, vehicle registries, passports, birth certificates, voter ids, gun permits, wills, escrows, degrees, car keys, house keys, patents, trademarks, coupons, genome data and even nuclear launch codes!
Companies like Ethereum and BitShares are now building their own, new block chains, platform and programming language to help developers build next-gen decentralized apps.
And just last week, a couple at Disney World had the first block chain marriage, recorded forever within the block chain!