Lotus Notes has been doing multi-master replication for over 20 years. The very architecture is built on it. Replication can be push-pull, push or just pull.

Lotus Notes has been doing multi-master replication for over 20 years. The very architecture is built on it. Replication can be push-pull, push or just pull. And can be scheduled or user-initiated. It automatically merges changed documents during replication. When the automatic conflict resolution fails, then it saves both copies and requires human intervention. Damien Katz (creator of couchdb) was a programmer for a core part of Notes until about 5 years ago. And Notes was the major influence on CouchDB. There are a ton of other good features in Notes (and a few bad ones too).