|Original author(s)||Colin LeMahieu|
|White paper||"Nano: A Feeless Distributed Cryptocurrency Network"|
|Initial release||4 October 2015|
|Latest release||V22.0 / 14 May 2021|
|Source model||Open source|
|Issuance schedule||Captcha faucet (ended)|
Nano (NANO), formerly RaiBlocks (XRB), is a peer-to-peer digital currency. It is a decentralized, open-source cryptocurrency based on directed acyclic graph (DAG) architecture, and released under the FreeBSD License. It operates without intermediaries by using a distributed ledger with a block-lattice data structure.[unreliable source?]
Nano was launched in October 2015 by Colin LeMahieu, with the aim of addressing blockchain scalability limitations that can result in restrictive fees and increased transaction confirmation times under load. It has feeless transactions that typically achieve full confirmation in under one second.
Development of Nano began in 2014 by Colin LeMahieu, under its original name of RaiBlocks. On 31 January 2018, RaiBlocks rebranded to Nano. Nano was distributed for free through a Captcha-based faucet which started in 2015. The faucet was shut down in 2017 after 126,248,289 NANO were distributed. Along with a 7,000,000 NANO developer fund, this fixed the total supply to 133,248,297 NANO. 
On 9 February 2018, the Italian cryptocurrency exchange BitGrail announced its shutdown after being hacked. There were unaccounted losses of 17 million Nano from its wallets, preventing users from accessing assets stored on the platform. The victims sought recoupment through the Italian court system, and supported by the Nano Foundation, launched a class-action suit against BitGrail owner Francesco Firano. In January 2019, the Court of Florence found Firano liable for the losses after discovering that the exchange had failed to implement any meaningful safeguards to ensure the safety of their customers' funds and failed to report losses from as early as July 2017.
Nano uses a block-lattice data structure, where every account has its own blockchain (account-chain).[non-primary source needed] It is the first cryptocurrency created on a directed acyclic graph (DAG),[unreliable source?] where a "block" is just one transaction, and each transaction contains the account's current balance.[unreliable source?]
Consensus is reached through an algorithm similar to proof of stake named Open Representative Voting (ORV). In this system, the voting weight is distributed to accounts based on the amount of NANO they hold: accounts then freely delegate this weight to a node of their choice. In the event that two contradictory transactions are broadcast to the network (as in a double spend attempt), nodes vote for one of them and broadcast their vote to the other nodes. The first transaction to reach 67% of the total voting weight is confirmed, and the other discarded.
This architecture allows Nano to function without direct monetary incentives to users or validators. Because certain entities benefit from the network indirectly (cryptocurrency exchanges through trading fees, merchants avoiding the fees associated with credit card companies, etc.), there is an interest to keep it healthy and decentralized by running a node. Since there is no direct incentive to accumulate voting weight, this also helps avoid the centralizing tendencies inherent to economies of scale such as traditional proof of work and proof of stake architectures.
Nano hopes to supplant Bitcoin as a more sustainable (ESG) cryptocurrency through legislation, regulation and climate advocacy.