Below are overviews and links to the four most-widely used Internet-based instant messaging tools and services. Keep in mind that not all IM software is compatible, and that users of one service may not be able to communicate with users of another. The recommended solution is to sign up for and install more than one of these products:

AOL Instant Messenger AOL's "AIM" software boasts perhaps the most intuitive user interface, and its instant messaging service features the largest number of subscribers. As with the other products, AIM offers real-time instant meesaging, multi-party chat, a list mechanism to keep track of your online friends and colleagues ("buddies"), and voice communication. One large drawback is that AOL's software is not compatible with that of other vendors. Available for the Windows, Macintosh, and Linux operating systems.

ICQ Regarded by many as the leader in multipurpose Internet-based communications tool, this full-featured program supports both synchronous (real-time) and asynchronous communication, including chat, message, e-mail, and file transfer. The program can be used in both a one-to-one (peer-to-peer) mode or in a multiple-user mode, so that groups can conduct online conferences. The software is compatible with other conferencing software, such as Microsoft NetMeeting and Netscape Cooltalk. Available for the Windows and Macitosh operating systems.

MSN Messenger Microsoft's software and related services encompasses instant messaging, chat, voice communication and phone calls, file-sharing, and online conferencing. Integrates easily with other Microsoft services, such as MSN.com and Hotmail. Available for the Windows and Macintosh operating systems.

Yahoo!Messenger This software is available from Yahoo!, the single most popular directory on the World Wide Web. The software supports all the basic functions--instant messaging, real-time chat, file transfer--and it integrates fully with Yahoo!'s content. The latest version also supports voice chat and telephony features (Windows 95/NT/98 only), as well as video. Available for the Windows, Macintosh, and UNIX operating systems.