multiple servers updating from/to one

Hi, all

I need to do this scenario:

Web Application           Web Application             Web Application
           |                                  |
              |
  pgsql server 1           pgsql server 2              pgsql server 3
           |                                  |
              |
           |                                  |
              |
           | adsl                          | adsl
         | adsl
           |                                  |
              |
           |                                  |
              |
              -------------------------------------------------------
                                              |
                             pgsql server ("master")

I need various servers in different locations running exactly some
things, one Web Application and one pgsql server, all synchronizing
with "master" server through unstable adsl connections.
So, If I do one insert in server 1, this data goes to "master" and is
available to other servers, and vice-versa, and if adsl connection
broken, Web Application still working with local server and when
connection is restored both databases are synchronized.
Is this possible?
If it's true, what tools I need?

Thanks in advance to any help, and sorry for my bad English (if
someone can't understand I say, I try to be more clear).

Cheers,

Marco Carvalho