The GeoServer project is a full transactional Java (J2EE) implementation of the OpenGIS Consortiums Web Feature Server specification. It is free software, available under the GPL 2.0 license. Users who would like to access and modify their geographic data over the Internet using flexible, industry-approved standards should take a look at GeoServer or one of the existing commercial Web Feature Servers. The GeoServer project is a Java implementation of the 1.0 Web Feature Server specification from the OpenGIS Consortium. GeoServer aspires to be the Apache of OpenGIS data serving and its mission is to enable greater geographic interoperability by enforcing OpenGIS standards and lowering the barriers to entry for geographic data providers.
Before you can use this GeoServer beta, you must successfully install Java, a Java Servlet container such as Resin or Tomcat, and PostGIS. This is by far the hardest part of the installation process, but the documentation to install these three components is quite good. Our testing has occurred on JDK 1.4.1, Tomcat 4.0.4, and PostGIS 0.7.3 on top of Postgresql 7.2.2. While installing PostGIS make sure to include the JDBC drivers in the PostgreSQL compile.
GeoServer has an active user community that you can engage by joining the GeoServer mailing list and asking questions or making suggestions. If you create a user account at this site, you may participate in forums and vote in polls as well.