PostgreSQL + Citus - multi master - replication of data
Answer compiled from part-answers originally left as comments

Citus is not a multi-master solution. It's a sharding solution. It does not replicate data. It distributes data between PostgreSQL instances. Read How Citus Works article for further information. - Sahap Asci

From Multimaster in the PostgreSQL Wiki (contributed by dezso):


  2ndQuadrant provides Bidirectional Replication for PostgreSQL (BDR). In this case updates can be performed at any node of the cluster and then propagated to other nodes. BDR is essentially asynchronous: changes are applied at nodes some time later after committing transaction at master and various ways of resolving conflicts are proposed. BDR is really fast (provides almost the same speed as hot standby), but certainly there is no global consistency in such model.