Chains of Git commits are already a blockchain - at least, already a DAG, and to...

Chains of Git commits are already a blockchain - at least, already a DAG, and to be more specific, they are both Merkle trees. Internally, each commit contains the hash of the previous commit it was based on:

    $ git cat-file -p HEAD
    tree e013f4d121199d60b70043f525aef4a7e641b5f6
    parent 152bbb43b30ced1b32e9ed6f5ba2ac448de725b6
    author Linus Torvalds <torvalds@linux-foundation.org> 1510512373 -0800
    committer Linus Torvalds <torvalds@linux-foundation.org> 1510512373 -0800

    Linux 4.14

You can even GPG sign each commit if you want to ensure authenticity. The other aspects of cryptocurrency blockchains don't really apply here: we don't need a single "true chain," in fact that's the point of branching.

(Kids these days with their blockchains...)