If 31-year-old Bill Gates, the billionaire head of Microsoft, is the boy wonder of the computer software world, then Frenchman Philippe Kahn, head of Borland International, is the enfant terrible.

Kahn is a strapping, irreverent man who refers to rival Microsoft's long-awaited OS/2 operating system as "BS2." He has made a huge success out of a simple idea: useful software at reasonable prices.

Borland is best known for the popular desk-top utility, Sidekick. But its greatest contribution has to be Turbo-Pascal, the $99 Pascal-language editor and compiler for IBM and compatible systems. It is now in its fourth edition, with greatly increased power and speed.

Turbo-Pascal has brought sophisticated programming power to the masses. It has also produced some remarkable software, much of it written by computer hobbyists and moonlighters who market their work as "shareware."

Shareware is the marketing concept in which programs are distributed free through computer user groups and bulletin boards. Commercial clearinghouses also sell it for a handling fee, usually about $5.

The author includes instructions in an accompanying disk file and requests that those who like the program send a registration fee, which buys extra benefits, usually a bound manual, free upgrades and, sometimes, telephone help. Fees rarely top $50 -- hundreds of dollars less than the prices of comparable commercial software.

So great is the Turbo-Pascal harvest that there is a program written and compiled with it for nearly every basic computer application. Some of the best: Galaxy: This word processor is simple to use, yet remarkably full-featured and blindingly fast. It offers a choice between working with drop-down menus or by keystroke commands. The commands will be familiar to anyone who knows Wordstar.

Galaxy executes search-and-replace operations faster than any program I have seen. It has no spell checker, but is designed to work with Borland's Turbo-Lightning, a very good and fast dictionary/thesaurus program. Galaxy is published by Omniverse, P.O. Box 2974, Renton, Wash., 98056, (206) 228-7627. The registration fee is $50.

Qmodem: This is one of the most popular modem communications programs in the IBM world. It is similar in operation to the classic PC-Talk III, which was the first shareware program. But Qmodem is much faster and more elegant, with windows and a host of file transfer protocols and terminal emulations.

Don't be put off by those technical terms. Qmodem is easy to use. Available from the Forbin Project, P.O. Box 702 Cedar Falls, Iowa, 50613, (319) 232-4516. The registration fee is $30.

Boyan: Another communications package, this is perhaps the best example of Turbo-Pascal's contribution. It was written by a high school student, Justin Boyan (he's now in college). Yet the program is good enough to have rated special mention in PC Magazine, which has otherwise paid scant attention to the shareware phenomenon.

Boyan is available from the author at 9458 Two Hills Court, Columbia, Md., 21045. Registration: $35.

As Easy As: This spreadsheet, as its name suggests, is a Lotus 1-2-3 workalike. It can read Lotus files, but it can't handle spreadsheets as big as those Lotus can. Still, it is fast and will do nearly everything Lotus can, including graphics.

As Easy As offers a choice between a Lotuslike command bar or a series of pull-down menus. From Trius Inc., 15 Atkinson Street, Lynn, Mass., 01905. The registration fee is $30.

Qubecalc and Instacalc: These two spreadsheets are among the only programs of their kind. Qubecalc is three-dimensional, allowing data to be examined and calculated from several perspectives. Instacalc is RAM-resident, which means it loads into your system's background memory and can be called up at the touch of a key while you're in the middle of another program.

Instacalc allows data to be pasted directly from the spreadsheet into whatever other program you're using. Both are from Formalsoft, P.O. Box 1913, Sandy, Utah, 84091, (801) 565-0971. Registration is $70 for Qubecalc, $50 for Instacalc.

PC-Deskteam: This is a memory-resident desk-top utility similar to Borland's Sidekick, except that Deskteam has more features. Its word processor is crude, but it has a typewriter feature that allows you to use your printer much as you would a typewriter. It also has a set of DOS commands built in, which can be most handy. From Alternative Decision Software, P.O. Box 307, Lancaster, N.Y., 14086. Registration is $20.

If you can't get these programs from a user group or bulletin board, here are some commercial libraries:

PC-SIG, 1030 E. Duane Ave., Suite D, Sunnyvale, Calif., 94086, (800) 245-6717. Public Library, P.O. Box 35605-P6, Houston, Tex., 77235, (713) 721-5205. Public Brand Software, P.O. Box 51315, Indianapolis, Ind., 46251 (800) IBM-DISK.

My last column on shareware brought an outraged complaint from a Macintosh user that it had left the impression shareware only existed in the IBM world. A good point. There is much good shareware for other computers, including the Macintosh.

Indeed, perhaps the best communications program for the Macintosh is Red Ryder, available as shareware or in stores for $69. A Macintosh shareware source is Educomp, 742 Genevieve, Suite D, Solana Beach, Calif., 92075, (800) 843-9497.

Brit Hume is a contributor to the Washington Post Writers Group. Hume is an ABC News Capitol Hill correspondent and the founding editor of a computer newsletter.