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.