PostGreSQL Replication

I know this is a delicate topic which must be approached cautiously.

Let's have a server which feed data to multiple slaves, usually using
direct online connections. Now, we may want to allow those client to
sync the data to a local replica, work offline and then resync the
data back to the server. Which is the easiest way to approach this
problem?

Can you address me to tools, documentation, tech reference or other
resource on this topic? I've found people talking about Slony-I, what
can you tell me on this tool? Are there other tools?

Moreover, additionally to the previous question, let's take the case i
do have multiple indipendent and separate server and then i want to
upload the information of these server (actually not everything but a
subset of the data) to another server (here we have a unidirectional
comm, as opposed to previous bidirectional comm and we have asymmetric
structure as opposed to the previous exact replica), what are the
tools, documentation, best practices or other resources to approach
this problem?

Thank you!