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.
Slony-I is a system designed for use at data centers and backup sites, where the normal mode of operation is that all nodes are available.
A fairly extensive "admin guide" comprising material in the Git tree may be found here. There is also a local copy.
