Several Web-Application-Servers work with PostgreSQL both open-source and commercial versions. The popular open-source Web-Application-Servers are Enhydra and Zope and commercial Web-Application-Servers are IBM Websphere, BEA Weblogic.
Enhydra supports PostgreSQL database. Enhydra is a immensely popular Java/XML Web-Application-Server created by 'Lutris Corporation'. It is the world's best Java/XML Web-Application server. It supports EJB, Servlets, JSP, JNDI, JDBC, JTA, CORBA, XMLC/Rocks, DODS and internationalization. It is written in 100% pure Java and is available from http://www.enhydra.org. Enhydra is a open source code project but is commercially sold and supported by Lutris Corp. Visit http://www.lutris.com
You would use Borland Corp's JBuilder along with Enhydra. JBuilder is at http://www.inprise.com
See also Enterprise Java HOWTO at http://www.linuxdoc.org/HOWTO/Enterprise-Java-for-Linux-HOWTO.html
Python is becoming immensely popular "pure" object-oriented scripting language. Zope is a Web-Application server and provides interfaces to PostgreSQL. Zope is available at http://www.zope.org Python is at http://www.python.org
OpenACS (Open ArsDigita Community System) http://openacs.org is an advanced toolkit for building scalable, community-oriented web applications. It relies on AOLserver, a web/application server, and PostgreSQL, a true ACID-compliant RDBMS. These are two high-quality products available for free under open-source licenses.
ACS is created by ArsDigita, http://www.arsdigita.com, their ACS (ArsDigita Community System) attempts to be as DB independent as possible, though it is based on Oracle (hence Open ACS have to take time out to port it).
See also http://www.appserver-zone.com