CRDTs (Conflict-Free Replicated Data Types)

Let two replicas edit the same data offline and merge with no coordination and no conflicts. Build the four canonical state-based CRDTs — a grow-only counter, a PN-counter, a last-writer-wins register, and an add-wins OR-Set — each with a commutative, associative, idempotent merge. The math behind Redis CRDTs, Riak, and collaborative editors.