Michael Rubenstein, an administrator at the University of Texas, and Air Force research and design engineer Captain Tom Speer both write microcomputer programs that they give away: Their free software for communications and printer graphics, respectively, are comparable to commercial products that cost $100 or more. In the past few years, programmers like Rubenstein and Speer have placed more than 40,000 programs into the public domain -- programs that can save the average company hundreds or even thousands of dollars.

Free doesn't mean inferior: Owners of everything from such discontinued machines as the Sinclair ZX-80 to lap portables like the Radio Shack Model 100 to desktops like the Kaypro, the IBM Personal Computer, and the Macintosh can pick from many first-rate databases, graphics packages, and communications programs. In addition, there are excellent spelling checkers, index markers, spread-sheets, and programs for printing documents. If managers aren't happy with their favorite commercial word processor or database system, there is a good chance that someone has written a piece of free software that solves the problem. There are free programs that reduce the size of the file to allow greater storage, and ones that rescue data from disks that have become unusable. There are games galore, and numerous versions of such programming languages as Logo, Forth, and C.

Since much of this software is good enough to sell, why does it end up in the public domain? One reason is idealism. Some programmers feel that software isn't a product to be sold, but a tool that should be shared. These electronic purists have a folk hero -- an IBM systems analyst named Ward Christensen. In 1977, he wrote the first widely used communications program for a microcomputer in his spare time -- now the legendary MODEM. As a "matter of principle," Christensen placed MODEM in the public domain. He could have made millions.

"I give away some of my programs because it's good business," says Rubenstein, who combines a consulting business with his academic duties. "Programs like OTERM405 [a communications program for the Osbornel] show potential clients how good I am." Captain Speer gives away PLOT33, a graphics printer program, for more altruistic reasons: to force down the cost of "overpriced" commercial software. Other programmers, like Dennis Brothers, the 38-year-old author of the first communications software for the Macintosh (MACTEP), initially write their programs to accomplish a task on a consulting job. Then friends start asking for copies. Eventually, the programmer decides that commercializing the software would be more trouble than it's worth. "So he does what I did with MACTEP -- he places it in the public domain," Brothers says. A program in the public domain can be freely used or copied, even if it is copyrighted by the author, as long as the user does not try to make any money from it, for example, by marketing the program to others.

There are a number of places where companies can go for free software. Compuserve, which has a large, free software section, and The Source, which has a much smaller one, both have excellent computer-based directories that list free software libraries, or bulletin boards. This system will transmit thousands of programs for the cost of a phone call. However, connect charges can mount up, since some of the best free databases and printer programs take up to an hour to download with a high-speed modem. Computer clubs are another source of software, because they tend to maintain large libraries of public-domain programs that members can copy free of charge. And clubs often swap programs with one another.

In addition to free software, microcomputer owners can find inexpensive user-supported software -- a unique hybrid between commercial and free programs. These programs, mostly written for IBM PCs, may be freely copied, but the authors ask "satisfied" users to pay a registration fee ranging from $10 to $75. In addition, some user-supported authors will license companies to produce unlimited copies of a particular program.

Andrew Fluegelman, the 40-year-old editorial director of PC-World and MacWorld magazines, pioneered the user-supported concept. His PC-Talk communications program for the IBM PC has the largest number of users -- about 8,000 have paid the registration fee (originally $25, now $35). He thinks that 10 times as many unregistered copies of PC-Talk are in circulation. Bob Wallace, the 35-year-old Seattle author of PC-Write, a lightning-fast word processor for the IBM PC and the IBM PCjr, likens the user-supported strategy to that followed by public television. "The program is freely distributed, but support from users is encouraged," Wallace says. So far, more than 3,000 people have paid the $75 registration fee; another 10,000 or so have sent Wallace $10 for a copy of his program.

The database program PC-File is one of the few user-supported programs that runs on generic MS-DOS machines as well as IBM PCs and true compatibles. PC-File (registration fee, $49) is the product of a former computer consultant in Seattle who uses the pseudonym Jim Button. At last count, Button had more than 11,000 registered users. He also offers three programs with registration fees that range from $29 to $48 -- PC-Dial (a communications program); an excellent spreadsheet, PC-Calc; and a program to graph data called PC-Graph.

Although the combined registration fees for PC-Write, PC-File, PC-Talk, and PC-Calc come to a stiff $200, a comparable quarter of commercial programs would cost six times as much, declares Alfred Glossbrenner, author of How to Get Free Software, the definitive Yellow Pages of sources. Glossbrenner advises anyone who is about to buy a computer to put off major software purchases until the noncommercial alternatives have been explored. Says Glossbrenner: "Get the operating system [the special program needed to run any other program on the machine] and maybe Basic, but for the rest, look into getting your first word processor, database, spreadsheet, and communications program from the public or the user-supported domain. Then if they're not good enough, buy."