What is Cumulus (Polkadot)?

Cumulus is an extension of the Polkadot Substrate development framework that allows Substrate-built runtimes to be compatible with Polkadot parachains through Polkadot's Relay Chain. A fundamental component of Cumulus is the Cumulus consensus engine, which is used to run a Polkadot node. This consensus engine is internally used to dictate to the node and synchronization algorithms which chain to follow, finalize, and treat as legitimate. Cumulus also makes use of Cumulus Runtimes to help enable validator nodes to work via Substrate and the system's block validator application programming interface (API). Finally, Polkadot Collators are also implemented via the Cumulus repository.