You can find the submodule for the multisig wallet contract code in this book's GitHub repository, in the Chapter10/MultiSigWallet directory. We are using the fork from the Gnosis multisig wallet repository. This repository may be updated with fixes and upgrades in the future.
In the MultiSigWallet project, Gnosis has built a DApp for the multisig contract that was built by ConsenSys. The smart contract was written by ConsenSys, and Gnosis built a good looking DApp for it. By using the DApp client, the wallet becomes very user-friendly, and anyone can create and use them. The only requirement for the multisig wallet DApp is that it needs MetaMask or a supported hardware wallet so that you can connect your account to it.
As we saw in the previous example, there were four signatories/owners of the multisig wallet...