The primary goal of b4 is to make it easier for maintainers to retrieve patch series, verify their authenticity, apply any follow-up code review trailers, and apply the patches to their maintained git trees.
This functionality works best when coupled with a public-inbox aggregator service, such as the one running on lore.kernel.org, but can be used with local mailboxes and maildirs, thus providing fully decentralized, experience with robust end-to-end attestation.
Working with patches sent to distribution lists
Patches sent to distribution lists remains the only widely used decentralized code review framework. RFC2822-conformant (“email”) messages adhere to an established standard that ensures high level of interoperability between systems, and it remains one of the remaining few truly decentralized communication platforms.
Note, that “distribution lists” may not necessarily mean “patches sent via email”. In addition to SMTP, RFC2822 messages can be also delivered via any number of push and pull mechanisms, such as NNTP, web archives, public-inbox repositories, etc. In the case of lore.kernel.org, the messages are collated from a large number of sources then replicated across multiple frontends.