Substrate is a web app development framework developed by Parity Technologies.
Substrate showcases an efficient database that developers can take advantage of in running and maintaining blockchain-based applications. It also supports a modular peer-to-peer networking stack capable of faster transaction throughput between blockchain networks and their participants. Moreover, it offers functions that can be configured according to the needs of an application, including transaction queues and runtime libraries.
Projects built using the Substrate can be easily deployed on the Polkadot ecosystem, helping them take advantage of the growing network for wider application adoption. Substrate also works flawlessly with any browser or desktop device.
As of now, Polkadot is one of the largest blockchain projects that utilize Substrate as the backbone of their network since it is the first protocol built on its framework. It needs to be noted that Substrate is not part of Polkadot and that anyone can build new blockchains that have nothing to do with the Polkadot blockchain. However, their DApps would still be compatible with Polkadot since they are built on the same framework. By and large, Substrate has been utilized mostly to build projects that advance the Polkadot ecosystem.