Remote Sync

I am currently in a situation where I have a distributed application between
a few remote nodes all connecting to a central database. I have been
searching for a database replication or synchronization system that will
allow a disconnected node to operate independently of the central database.
The ultimate intention of this type of system is to have an application
operate off of data locally and have those changes synced in the background.

From the research I've done, Slony doesn't support multi-master writers.
PGCluster and ExtenDB seem to require all nodes be next to each other with
the ultimate goal of local load balancing.

Are there any solutions that come close to the requirements I'm after?

Thanks for any input,

-Daniel