Redundancy software for PostgreSQL

Hello Forum,

I would appreciate it if you could recommend software to build redundancy in
my application (my application stores data in a PostgreSQL v7.3.x database
running in Linux RedHat) The software would replicate or copy the database
from a main server into a second server. And when the main server goes
down, the redundant database could still be available in a view mode --
where most tables cannot be updated and only a couple of tables can be
modified. In this way, when the main server goes down, the users could
still view data and when the main server goes back on-line, I can update a
couple of tables of the main database with the data from the redundant
database.

Thanks in advance for your response.