One idea me and my brother messed about with was "Merkel DAGs". The place we worked at had, what amounted to, a really fancy workflow/flowchart designer and the question was always how to make it collaborative (because that would sell like hotcakes on a slide deck, irrespective of whether people used it). Another concern was versioning, and Git is a Merkel DAG; great problems think alike.

We never finished it because of some truly difficult questions, and decided that failure was the most reasonable result. There were some truly awesome things though. For example, if two users independently connected the same two flowchart steps with the same two lines, those two changes would be understood as identical by the system (by nature/emergence). It was also very granular snapshot consistency, which is incredibly simple to reason about.

The other cool thing was that CAS (again, a Git concept) is absurdly cache friendly, and all forms of fancy stuff can be done there.

We ultimately failed it because we had messed up somewhere and wound up with tons of borderline cases (and the hope was that we wouldn't need them). I still think, given the absence of our mistakes, it could work and would be really elegant code.