PostgreSQL is designed to be easily extensible. For
this reason, extensions loaded into the database can function just
like features that are packaged with the database. The
contrib/ directory shipped with the source code
contains a large number of extensions. The README file
in that directory contains a summary. They include conversion
tools, full-text indexing, XML tools, and additional
data types and indexing methods. Other extensions are developed
independently, like PostGIS. Even
PostgreSQL replication solutions are developed
externally. For example, Slony-I is a popular
master/slave replication solution that is developed independently
from the core project.
There are several administration tools available for
PostgreSQL. The most popular is
pgAdmin III,
and there are several commercially available ones as well.