Blockchains, or block chains, are decentralized databases that record and verify transactions securely and transparently using cryptography and consensus among users. Each transaction is recorded in a block that is added to the chain, forming an immutable sequence of information.

Among the most important blockchains are:
Bitcoin: The first blockchain created in 2009 for the Bitcoin cryptocurrency. It is the best known and used worldwide, and its main objective is the transfer of value without the need for intermediaries.
Ethereum: Created in 2015, it is a blockchain that allows the creation of decentralized applications and smart contracts. It is used for the creation of tokens and for the development of DeFi projects (decentralized finance).
Binance Smart Chain: Created in 2020, it is an Ethereum-compatible blockchain that offers fast and cheap transactions. It is used by many DeFi projects due to its high interoperability.
In addition to the aforementioned blockchains, there are others that have gained relevance and popularity in the world of cryptocurrencies and blockchain technology. Next, I describe the following 7 most important blockchains:
Cardano: Created in 2015, it is a blockchain that focuses on security and scalability. It uses a consensus algorithm called Ouroboros and aims to offer solutions in different areas, such as digital identity and product traceability.
Polkadot: Created in 2019, it is a blockchain that focuses on interoperability between different blockchains and decentralized systems. It uses a protocol called Substrate and aims to offer a platform for the development of decentralized applications.
Solana: Created in 2017, it is a blockchain that focuses on speed and scalability. It uses a consensus algorithm called Proof of History and aims to offer a platform for the development of high-performance decentralized applications.
Ripple: created in 2012, it is a blockchain that focuses on the transfer of value through its cryptocurrency XRP. It uses a consensus protocol called Ripple Protocol Consensus Algorithm and aims to offer solutions in the financial field.
Tron: Created in 2017, it is a blockchain that focuses on creating a platform for online gaming and entertainment. It uses a consensus algorithm called Delegated Proof of Stake and aims to offer solutions in the field of entertainment industry.
EOS: created in 2017, it is a blockchain that focuses on the scalability and performance of decentralized applications. It uses a consensus algorithm called Delegated Proof of Stake and aims to offer a platform for the development of high-performance decentralized applications.
Stellar: Created in 2014, it is a blockchain that focuses on the transfer of value through its Lumens cryptocurrency. It uses a consensus protocol called Stellar Consensus Protocol and aims to offer solutions in the financial field and international remittances.
Each of these blockchains has its own focus and goals, and they have gained prominence in different areas and markets.