The latest software, documentation and news items are available at the PostGIS web site, http://postgis.refractions.net.
More information about the PostgreSQL database server is available at the PostgreSQL main site http://www.postgresql.org.
More information about GiST indexing is available at the GiST development site, http://www.sai.msu.su/~megera/postgres/gist.
More information about Mapserver internet map server is available at http://mapserver.gis.umn.edu.
The "Simple Features for Specification for SQL" is available at the OpenGIS Consortium web site: http://www.opengis.org.