`git` is a content-addressable filesystem (the "plumbing") with a VCS UI on top of it (the "porcelain"). `jj` is alternative "porcelain" using the same "plumbin

`git` is a content-addressable filesystem (the "plumbing") with a VCS UI on top of it (the "porcelain"). `jj` is alternative "porcelain" using the same "plumbing". Git was initially designed to be a toolkit on which to create VCSes, over time the VCS portion of Git has become more complete but is still a very leaky abstraction, resulting in users having to use the "plumbing" commands more often than never. `jj` aims to be better "porcelain" over the Git "plumbing", and the project authors hope to eventually support other "plumbing" model(s).