HTML 2.0
Current approved version
All current browsers support 2.0
Basic functionality seen in most documents on the WWW today

HTML 3.0 (HTML+)
Current browsers support most of 3.0 (table and math support varies)
Major changes from 2.0, including: richer image features, tables, mathemathical formulas, style

JavaScript
Javascript is Netscape's cross-platform, object-based scripting language for client and server applications.
Client-side Javascript statements embedded in an HTML page can respond to user events such as mouse-clicks, form input, and page navigation. For example, you can write a javascript function to verify that users enter valid information into a form requesting a telephone number or zipcode.

Java
Created by Sun Microsystems. Considered a programming language
An object oriented programming language that can be used to create interactive applets.

Perl
By far the most popular language for CGI (Common Gateway Interface), because, among other things, it has powerful string matching. It is an interpreted language optimized for scanning text files, extracting information from those files, and printing reports based on that information. It's also a good language for many system management tasks.

CGI
CGIs permits interactivity between a client and a hosting operating system through the World Wide Web via the HTTP protocol. It's a standard for external gateway programs to interface with information servers, such as HTTP or Web Servers.