[srjk]

I've used unison in the past and liked it. May not fulfill the "zero knowledge" criteria but IIRC it's fairly simple to set up.

http://www.cis.upenn.edu/~bcpierce/unison/

[StavrosK]

Unison does fulfill the zero-knowledge criteria, but it's not a daemon that runs constantly, although I might give it a shot, thank you.