2ndQuadrant's "pluggable" multi-master replication for PostgreSQL. In production use with major embedded systems manufacturer.
The twin (multi-master replication)project is a PostgreSQL Community project that is a part of the pgFoundry.
The pgFoundry page for the project is at http://pgfoundry.org/projects/twin, where you can find downloads, documentation, bug reports, mailing lists, and a whole lot more.
