Pijul's "upstream" (and git predecessor) darcs is still useful today. It doesn't see itself as a "research prototype" and has decades of experience in the real world. It isn't git compatible but does offer a fine fast-export to git in the worst case you need to switch.

Unfortunately some of those decades of experience with darcs are lessons in how it performs poorly in large repos or with large teams/lots of merge conflicts, but that still leaves darcs a good experience for small projects and "just getting stuff done".