Cosmos

Cosmos is a blockchain and cryptocurrency (ATOM) for creating an ecosystem of interoperable blockchains. The team aims to "create an Internet of Blockchains, a network of blockchains able to communicate with each other in a decentralized way." Cosmos is similar to Polkadot in its mission but they each take a different approach to transaction validation and token transfer.

Cosmos has a proof of stake system in which the top 100 highest stakers validate the transactions in their “hub”. Blockchains created with Cosmos (zones) can have their own different validation system. In Polkadot, parachains are like zones, but they can’t choose their own validators - they all rely on the validators of the Polkadot Relay chain, offering unified security at the expense of less flexibility.

When there is a transaction across blockchains, Cosmos uses the Inter Blockchain Communication Protocol and the Cosmos Hub to record transactions in three places, the two chains and the central hub. Polkadot uses the Relay Chain to execute smart contracts to move the tokens.