Blockstream App supports layer-2 Bitcoin networks that offer features and advantages not found on the base blockchain. Currently, Blockstream App has integrated with both the Lightning Network and the Liquid sidechain.
Lightning
Bitcoin's Lightning Network enables much cheaper and faster transactions than what is possible on the Bitcoin blockchain. This layer-2 network leverages various Bitcoin smart contracts to create a network of cached transactions that can be made instantaneously at a low cost before eventually settling back on the base Bitcoin blockchain.
The low fees and fast pace associated with Lightning Network transactions makes them ideal for lower-value payments such as tipping a content creator online or buying coffee.
Liquid
The Liquid network is a federated sidechain for Bitcoin that enables faster block times, tokenization, more private transactions, and other additional functionality. The world's largest stablecoin, Tether, is available on Liquid, and trustless swaps can be made between Tether and bitcoin in a non-custodial manner. New smart contract functionality is also sometimes found on Liquid before it makes its way to Bitcoin.
Note: Although Liquid and the Lightning Network are both referred to as a layer-2 networks, the Lightning Network can also operate on top of the Liquid sidechain in the same manner it does on top of the base Bitcoin blockchain. In fact, Liquid is sometimes used as a cheaper alternative to the Bitcoin blockchain for adding liquidity to the Lightning Network.