How do you build a thriving commercial software business out of software that's available under the GNU General Public License? Trolltech's strategy is to offer customers a choice: a GPL version at no charge or a version compatible with proprietary software at a fair price.

If anyone has put money and time into useful software for embedded Linux, it's Trolltech. Normally bad-tempered C++ programmers consider the company's cross-platform Qt toolkit to be a thing of beauty. I talked with Haavard Nord, cofounder and CEO of Trolltech, on the occasion of the initial public release (version 1.5) of Qtopia, the Qt-based operating environment that has the sheer chutzpah to be a Third Way in PDA platforms--in direct competition with Palm and Microsoft's Pocket PC. How does a small company like Trolltech possibly expect to pull off something like that?

The answer, Nord says, is that device vendors ``want to compete in making state-of-the-art hardware''. Not everybody wants to be in the Pocket PC business, making generic Pocket PCs.

The Sharp Zaurus PDA, already extensively covered here, will be the first Qtopia product on the market, and others to follow will include digital cameras with a Qtopia application for e-mailing photos and a Qtopia ``smart phone'', Nord says. A startup, Vercel, also plans to make Qtopia devices. ``It was founded by the guy who created the Furby. He's a genius'', Nord adds. ``The user interface is going to be very exciting. It's going be something you've never seen before. They're doing the same thing Transmeta did when they launched their web site--they're showing very little.'' (Let's just hope their business plan doesn't involve another goofy little scooter for people who dress up as Devo and try to ride on the sidewalk.)

But with all that wild and woolly originality out there, how can there be a critical mass of software that works with every Qtopia product? ``We are working with companies like Lineo and MontaVista to design a standard binary format for ARM processors'', Nord said. In practice, the Zaurus was there first, and its binaries should become the de facto standard, he added.

So how does the GPL tie into all this? Well, you can get the Qtopia libraries and tools under GPL, which means your project linked with the libraries is GPL, too. If you're doing purely free software, that's not a problem. If your software business model is different, get out your checkbook and pay a very reasonable $200 for the commercial SDK.

Nord says the dual-licensing system, reached after a brief attempt at a GPL-like but incompatible license, is working very well. The KDE Project, which uses Qt on the desktop, is thriving, and the availability of a free SDK for Qtopia means that many developers are porting KDE applications over to Qtopia, Nord says.

The dual-licensing model gives buzz, ubiquity and developer familiarity on the GPL side and revenue on the proprietary side. ``For us, it helps us distribute our technology under an open-source license, a free-software license, and it also gives us an opportunity to make revenue. So the GPL is a useful license, I think'', Nord said.

The embedded Linux developers of the world have a lot of good stuff for you this issue. If you've been following Kevin Dankwardt's series on real-time performance under Linux, check out the thrilling conclusion where he benchmarks the sub-kernel approach on page 33. Yes, you can start calling Linux an RTOS now. In our cover story (page 19), Rick Lehrbaum breaks through another confusing issue--the incredible diversity of single-board computers. You won't be able to pick one, but at least you'll be able to narrow your choices down a little bit.

We've had quite a lot of action in the contest department this month, with final winners being chosen in the NIC contest and finalists in the Linux4.TV contest. See what most people would never expect to do with a thin client or a consumer appliance on pages 8 and 10.

Kernel hacker Greg Kroah-Hartman sent us such a long list of device-driver topics he wants to write about that we just made him our device-driver columnist. His column, ``Driving Me Nuts'', will start next issue. This issue, check out his rules of cross-platform driver compatibility on page 28.

There's a lot of other useful stuff in this issue too, so don't forget to take it to work and pass on the subscription card to someone else who might be interested.

For free software and contributions using Qt, see http://www.trolltech.com/developer/freesoftware/index.html.