other language interfaces are external projects and are distributed
   separately. A
   <ulink url="https://wiki.postgresql.org/wiki/List_of_drivers">list of language interfaces</ulink>
   is maintained on the PostgreSQL wiki. Note that some of these packages are
   not released under the same license as <productname>PostgreSQL</productname>.
   For more information on each language interface, including licensing terms,
   refer to its website and documentation.
  </para>

  <para>
    <ulink url="https://wiki.postgresql.org/wiki/List_of_drivers"></ulink>
  </para>
 </sect1>

 <sect1 id="external-admin-tools">
 <title>Administration Tools</title>

  <indexterm>
   <primary>administration tools</primary>
   <secondary>externally maintained</secondary>
  </indexterm>

  <para>
   There are several administration tools available for
   <productname>PostgreSQL</productname>. The most popular is
   <application><ulink url="https://www.pgadmin.org/">pgAdmin</ulink></application>,
   and there are several commercially available ones as well.
  </para>
 </sect1>

 <sect1 id="external-pl">
  <title>Procedural Languages</title>

  <indexterm>
   <primary>procedural language</primary>
   <secondary>externally maintained</secondary>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname> includes several procedural
   languages with the base distribution: <link
   linkend="plpgsql">PL/pgSQL</link>, <link linkend="pltcl">PL/Tcl</link>,
   <link linkend="plperl">PL/Perl</link>, and <link
   linkend="plpython">PL/Python</link>.
  </para>

  <para>
   In addition, there are a number of procedural languages that are developed
   and maintained outside the core <productname>PostgreSQL</productname>
   distribution. A list of
   <ulink url="https://wiki.postgresql.org/wiki/PL_Matrix">procedural languages</ulink>
   is maintained on the PostgreSQL wiki. Note that some of these projects are
   not released under the same license as <productname>PostgreSQL</productname>.
   For more information on each procedural language, including licensing
   information, refer to its website
   and documentation.
  </para>

  <para>
   <ulink url="https://wiki.postgresql.org/wiki/PL_Matrix"></ulink>
  </para>
 </sect1>

 <sect1 id="external-extensions">
 <title>Extensions</title>

  <indexterm>
   <primary>extension</primary>
   <secondary>externally maintained</secondary>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname> is designed to be easily extensible. For
   this reason, extensions loaded into the database can function
   just like features that are built in. The
   <filename>contrib/</filename> directory shipped with the source code
   contains several extensions, which are described in
   <xref linkend="contrib"/>.  Other extensions are developed
   independently, like <application><ulink
   url="https://postgis.net/">PostGIS</ulink></application>.  Even
   <productname>PostgreSQL</productname> replication solutions can be developed
   externally. For example, <application> <ulink
   url="https://www.slony.info">Slony-I</ulink></application> is a popular
   primary/standby replication solution that is developed independently
   from the core project.
  </para>
 </sect1>
</appendix>