Third-party replication tools that replicate based on SQL triggers running on the primary server(s).
Bucardo is an asynchronous PostgreSQL replication system, allowing for both multi-master and multi-slave operations. It was developed at Backcountry.com by Jon Jensen and Greg Sabino Mullane of End Point Corporation, and is now in use at many other organizations.
Bucardo is free and open source software released under the BSD license.
PgQ is a queuing system written in PL/pgSQL, Python and C code. It is based on snapshot-based event handling ideas from Slony-I, and is written for general usage.
Londiste is a replication tool written in Python, using PgQ as event transport.
Mimeo is an extension that provides specialized, per-table replication between PostgreSQL instances. It currently provides snapshot (whole table copy), incremental (based on an incrementing timestamp or id), and DML (inserts, updates and deletes).
Slony-I is a "master to multiple slaves" replication system for PostgreSQL supporting cascading (e.g. - a node can feed another node which feeds another node...) and failover.
The big picture for the development of Slony-I is that it is a master-slave replication system that includes all features and capabilities needed to replicate large databases to a reasonably limited number of slave systems.