Conflict-free replicated data type (CRDT) is super interesting data type (and algorithm), especially when it is implemented for complex data structures like JSON: A JSON CRDT is "[...] an algorithm and formal semantics for a JSON data structure that automatically resolves concurrent modifications such that no updates are lost, and such that all replicas converge towards the same state (a conflict-free replicated datatype or CRDT)." [1].

[1] A Conflict-Free Replicated JSON Datatype (https://arxiv.org/abs/1608.03960) b Martin Kleppmann and Alastair R. Beresford.