The capability of the Web has been greatly enhanced with the addition of plug-ins. Plug-ins are small pieces of software that integrate with Web browsers to greatly enhance their features. There are more than a thousand different plug-ins available today, which are also sometimes often called "players." Plug-ins are generally available free of charge, and can be downloaded easily from the Internet. Many plug-ins facilitate the use of multimedia, others enable the viewing of special documents, and still others enable links to proprietary databases and graphing tools.

Because plug-ins are developed by many independent companies, for each desired functionality there will be a variety of plug-ins to choose from. Among the common plug-ins used for WBT today:

• Shockwave, from Macromedia, enables multimedia programs created in Director and Authorware to be played via an Intranet and the Internet.

• Flash, also from Macromedia, greatly accelerates the display of most graphics and animations on the Web, and enables for streaming audio as well. Flash is commonly used for images within tutorials, as well as to add visual cues to user interfaces, such as highlighting buttons and other clickable areas when the mouse cursor moves over them. Flash is now included in Microsoft's Internet Explorer 5.0 browser and has become the Internet standard for Web-based multimedia.

• Acrobat, from Adobe, is a document-formatting standard. The Acrobat reader is a plug-in that enables you to download and view documents in a format that is true to their original hard-copy appearance.

• RealPlayer, from Real Systems, enables viewing of streaming video and audio clips.

It is a good idea to make sure your student audience has the necessary plug-ins prior to deliverying an e-learning program that is dependent on them. If students access the program without the required plug-in, all they will see is an error message, or slightly better, instructions on how to download the required plug-in assuming it is free of charge. Designers should also be aware that just because a student's browser has a plug-in does not necessarily mean you should use multimedia on the Web, because the other dependent variable is the student's available bandwidth.