1. W3C HTML Validator
Free Perl script for HTML validation.

2. Mozilla - XML/HTML browser
Official website with information and downloads.
www.mozilla.org

3. PHP: Hypertext Preprocessor
PHP is a server-side HTML embedded scripting language. It provides web developers with a full suite of tools for building dynamic websites: native APIs to Apache and other web servers; easy access to MySQL, Sybase, Oracle, and other databases; IMAP; LDAP;
www.php.net

4. Java.com
A resource for Java technology consumers, with a focus on Games.
www.java.com

5. Drupal
An engine suitable to setup or build a content driven or community driven website. Modular design allows flexibility in design.
drupal.org