Blockstream is a private, for profit, blockchain technology company, that has played a key role in helping to develop, and fund, many of the key features of the Bitcoin Core platform. Blockstream is focused on developing bitcoin applications and has raised significant funding from several large investment funds. The company also employs several developers that are very influential within the Bitcoin Core development project. This, as well as being of Bitcoin's largest donors, has led to some criticism about conflicts of interest.
Blockstream is developing a number of Bitcoin applications that are intended to encourage adoption and improve transaction times on the bitcoin network. Their primary focus is on Sidechains, which are are extensions to existing blockchains that improve their functionality. The company is also working closely with industry leaders to create the Bitcoin Lightning system that will support higher trading volume and faster transactions on the bitcoin network. Blockstream is also developing a data feed, satellite network, and other applications that they hope will make blockchain more accessible.

QuarkChain is building a blockchain with a focus on speed and scalability. They hope to significantly improve transaction times and reduce fees with an architecture that will rely on a two-layered blockchain and elastic sharding. QuarkChain uses a hybrid Proof-of-Work (PoW) consensus mechanism that is ASIC-resistant. Transactions are first confirmed on one blockchain layer, and then on the second. The network will be powered by the QKC coin.