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Bitcoin
Bitcoin usage worldwide.
Bitcoin is a decentralized digital currency that enables instant payments to anyone, anywhere in the world. Bitcoin uses peer-to-peer technology to operate with no central authority: transaction management and money issuance are carried out collectively by the network.

The original Bitcoin software by Satoshi Nakamoto was released under the MIT license. Most client software, derived or "from scratch", also use open source licensing.

Bitcoin is the first successful implementation of a distributed crypto-currency, described in part in 1998 by Wei Dai on the cypherpunks mailing list. Building upon the notion that money is any object, or any sort of record, accepted as payment for goods and services and repayment of debts in a given country or socio-economic context, Bitcoin is designed around the idea of using cryptography to control the creation and transfer of money, rather than relying on central authorities.

Bitcoins have all the desirable properties of a money-like good. They are portable, durable, divisible, recognizable, fungible, scarce and difficult to counterfeit.

Why?
Bitcoin is P2P electronic cash that is valuable over legacy systems because of the monetary autonomy it brings to its users. Bitcoin seeks to address the root problem with conventional currency: all the trust that's required to make it work -- Not that justified trust is a bad thing, but trust makes systems brittle, opaque, and costly to operate. Trust failures result in systemic collapses, trust curation creates inequality and monopoly lock-in, and naturally arising trust choke-points can be abused to deny access to due process. Through the use of cryptographic proof, decentralized networks and open source software Bitcoin minimizes and replaces these trust costs.
Bitcoin Transactions are:
Permissionless and borderless. The software can be installed by anybody worldwide.
Anonymous. Bitcoin does not require any ID to use making it suitable for the unbanked, the privacy-conscious, computers or people in areas with underdeveloped financial infrastructure.
Private. When used with care bitcoin can support strong financial privacy.
Censorship-resistant. Nobody is able to block or freeze a transaction of any amount.
Fast. Transactions can be made almost as fast as data can travel over the Internet.
Cheap. Fees can be very very low.
Irreversible once settled, like cash. (but consumer protection is still possible.)
Online and available 24 hours a day, 365 days per year.
Bitcoin can also be a store of value, some have said it is a "swiss bank account in your pocket".

Stored Bitcoins:
Cannot be printed or debased. Only 21 million bitcoins will ever exist.
Have no storage costs. They take up no physical space regardless of amount.
Are easy to protect and hide. Can be stored on a phone, computer, encrypted on a paper backup or memorized in your head.
No counterparty risk. If you keep the private key of a bitcoin secret and the transaction has enough confirmations, then nobody can take them from you no matter for what reason, no matter how good the excuse, no matter what.
Can be under divided possession with Multisignature. For example with a 2-of-3 multisig scheme there would be three private keys, of which any two is enough to spend the money. Those three keys can be spread anywhere, perhaps in multiple locations or known by multiple people. No other asset does this, for example you cannot hold gold coins under multisig.