• Webserver software of any kind, Apache recommended but run also on Lighttpd very well.
• PHP scripting language.
  
  You need PHP 5.0 or newer, with session and database support.
  
  CURL module if you want authenticate users via GMail account.
• MySQL, PostgreSQL, or SQLite database
  
  MySQL version 3.23 or newer.
  
  PostgreSQL version 8.1 or newer.
  
  SQLite version 2. Don't work with version 3.
• Web browser with cookies and javascript enabled.
• An absolute minimum of 17Mb of disk space (24Mb for initial installation).

The Apache webserver can be downloaded from the Apache project at http://www.apache.org
MySQL database software can be obtained from http://www.mysql.com
PostgreSQL database software can be obtained from http://www.postgresql.org
and PHP from http://www.php.net if you are building your own server.

Complete LAMP (Linux, Apache, MySQL and PHP) platforms are:

• XAMPP - for almost all operating systems
• MAMP - for MacOSX